meow1917's Doom tips and tricks!!

What you gotta know

You'll figure most of these out after playing for a while but keep scrolling even if you've got the chops, because there's stuff even long-time players don't realise down there! Remember, the only way to get better is to keep playing! ✨

Actors have infinite height

This one gets thrown about quite a bit about how Doom is 'technically a 2D game' and such, but in reality, Doom is a 3D game that sucks at being 3D. 😜

• You can't jump over or walk under monsters.
• You can be damaged by a monster next to but much below or above you.
• Splash damage will hurt all monsters at a spot, no matter how high or low.

This means you should beware lifts with monsters on other storeys and you can shoot at walls to clear monsters below them. Now, keep in mind that most source ports will have a way to work around the infinite height issue but you'll get mauled to death with mêlée attacks if you try to crowdsurf monsters, hehe.

Autoaim will vertically aim your attack on the nearest target

This one's quite obvious... You can't look up or down (or jump or crouch) in vanilla Doom but the game helpfully points your attacks up and down to the nearest monster right in front of you. Keep in mind that autoaim just gives up and stops working after 1024 units, so you can always cheat by enabling free look to snipe far away monsters hehehe...😝

Cyberdemons and spider masterminds are invulnerable to splash damage

Yep, that's why E2M8 is a chore! Always use plasma weapons (plasma gun and BFG 9k) against da big bosses. Or better yet, get the spider mastermind to hurt her grunts with her hitscan attack and watch them do her in! 😉 But if you're keen, you'll notice that cyberdemon isn't the only monster that deals splash damage. Indeed, the archvile isn't immune to his own attack's blast and is the only monster that can kill itself with its own attack by targeting nearby monsters! Silly boy.

Monsters are not hurt by the types of projectiles they shoot

Exactly what it says on the tin. Imps can't hurt other imps. Hell knights and barons of hell can't hurt each other and so on, so you can't get them to infight. But hitscan attacks hurt everyone and all monsters will retaliate to hitscan attacks. Monster mêlée is a special kind of attack that can hurt everyone but monsters will never mêlée each other on accident. (Fists and chainsaw are still hitscan.) You can play peekaboo with large groups of zombiemen to get them to kill each other! 😈

Monsters can't infight pain elementals

Ten points if you can guess why. If you said 'because they'll be infighting the lost souls instead,' you got it right! But keep in mind that pain elementals will focus on monsters that hurt them and can quickly fill up sectors with lost souls if you don't intervene...

Monsters won't infight archviles

I bet you can never guess why... 😉 It's because they're hardcoded as uninfightable (is that even a word?) in the game code. It also means an archvile can't 'infight' himself even if he hurts himself with splash damage. But he will nevertheless happily zap away helpless mooks for hurting him.

Lost souls will forget their targets after attacking once

Seems like there's no brain in that skull because these annoying jerks will forget whom they were angry at after charging once and go back to focusing on you! So if a pain elemental is infighting another monster, you've got a mess to clean up.

Cyberdemons, spider masterminds, archviles, lost souls and pain elementals cannot be resurrected

Thank goodness! Oh and crushed monsters can still be resurrected, unlike in Quake II. Resurrected gibs turn into ghost monsters in vanilla source ports where they are only hurtable with splash damage. Spooooky~ 👻

Berserk lasts until the end of the level

Because you stop seeing red after a while, n00bs think berserk goes away after a while but it actually lasts until the end of the level... Or not! It actually lasts about 4 years (for real!) but you'd probably finish the level under that par time no matter how n00bish you are heheh.

Green armour (⅓ protection) and blue armour (½ protection) replace each other when picked up.

Yup yup, stay away from green armour unless your blue armour is running, like, super low. Oh and armour bonus gives green armour if you had no armour.

Slow crushers are inescapable without invulnerability

There are two types of crushers: Fast crushers don't give a cat's whiskers if anything's standing under them and just give you a good bonk of 60 damage. But slow crushers will slow down once they reach you and won't let you go. If you're caught, you're doomed (no pun intended) because they will inflict a whopping 940 damage in total!!

If you're caught under two crushers at once, the damage is exponential

I've never had this happen to me but if you somehow manage to get in such a situation, you probably deserved it. 🥴

Weapons and ammo can get crushed

Everyone knows if you leave a corpse under a door or on a lift, it turns into gibs. But did you know that if you leave a weapon or some ammo there, it gets 'crushed' too? (It simply disappears!)

You can telefrag monsters but monsters cannot telefrag you (outside M30 of Doom 2) or each other

Monsters spawned by the cube, monsters respawned in Nightmare! difficulty, and monsters revived by archviles can telefrag you in M30. Players can telefrag each other in deathmatches regardless of the map. Otherwise, the player is immune to telefragging.
Standing on an exit teleporter will instead block it and prevent monsters from teleporting in, which is a useful tactic for stalling the influx of monsters.

Invulnerability only protects up to 1000 damage at a time

You thought you were totally safe? Nope, the invulnerability won't stop attacks that hurt more than 1000 hit points at a time. Fortunately, no such damagers exist in vanilla Doom, right? Oh wait, you can still get telefragged in M30 or deathmatches, what's up with that? It's because telefragging inflicts... wait for it... 10 000 damage! That's right, nothing can protect you from telefragging (save for Pentagram of Protection demon magics in Quake).

Damaging floor only hurts if your centre point is on a damaging sector

If you hang off the edge of a damaging floor platform, you can avoid taking damage without falling down as long as your centre point is in the neighbouring sector.

Rad suits can randomly leak on 20% damaging floor

Yeah, you aren't imagining things! There are four types of hurty floors: Nukage (5%), hellslime (10%), strobe (20%) and super hellslime (20%). There's an itsy bitsy chance (2,3%) each tic that strobe and super hellslime floors seep through your rad suit and hurt you. What are they making these suits out of anyway?

Pain elementals will not spawn lost souls if there are at least 21 alive

Unfortunately, nearly all source ports remove this limit, making pain elementals a force to be reckoned with that can fill up entire sectors with their super annoying hell spawn! 👿

Pain elementals will not shoot lost souls if you hug them

Goes to show that there's nothing you can't overcome with a little bit of love~! Well, to be fair literally anything blocking them can stop them from shooting lost souls (and you can even walk into their death animation to the same effect in some source ports) but I like my interpretation better, ehe~!

Shotgun spread is horizontal, whereas super shotgun spread is circular

As great as the SSG is for close-range combat, you should make use of the pump-action shotgun's tighter and horizontal spread to snipe off firing squads at long range. At a closer range, it's still useful for shooting into horizontal windows/slits on walls.

BFG shoots hitscan tracers the moment the projectile lands, in the direction of the projectile

N00bs struggle with this a lot but you gotta grok the big flippin' gun to be a pro. You pull the trigger, the projectile gets cooked and pew it goes. Once it hits a monster (or a wall or anything), your body shoots a cone of hitscan tracers (like a big phat shotgun) exactly in the direction you shot the projectile (even if you moved away, turned elsewhere and switched to a different weapon!) that perforate anything in their way. Pew!
Check out The BFG FAQ for more detailed information.

Weapons make 'sounds' only the moment the trigger is pulled

It sounds super silly but the sounds only propagate in the sector the trigger is pulled in. That means you can pull the BFG trigger in a room, dash into another room with sound-blocking walls and blast at monsters whilst unhurt monsters that don't see you keep sleeping in the same room! It even works across teleporters: You can prefire a rocket or BFG before taking a teleporter and silently blast out of the exit teleporter.

Only your weapons' sounds can wake up idle monsters

That's right, this even applies to the your fists' gentle whooshing in the air. They won't give a cat's whiskers about other monsters' attacks! They will also wake up if they see you or if they get hurt because, c'mon, who wouldn't? (For some reason, they will keep sleeping if you only hit them on their second idle frame and don't trigger a pain state, however.)

Monsters will be paralysed if they have nowhere to move when they wake up for the first time, are infighting, or have an unreachable target

You can paralyse a monster satisfying one of these conditions by blocking all the eight directions they can move (hug them in a corner!) and it will politely stay paralysed for you to kill it! The paralysis doesn't last for ever, mind you, about 1,5 hours, actually.

Monsters with both mêlée and ranged attacks can convert one to the other depending on the target distance

All projectile monsters also have a mêlée attack (save for mancubi and cyberdemons). If you get close to them, imps will scratch you, cacodemons will bite you and hell nobles will pummel you. If you get close to a monster whilst it's 'cooking' its projectile attack, it will turn the attack to mêlée and hit you instead. Similarly, if you stand back just as you're about to get hit, it will immediately shoot out a projectile. Revenants are a notable exception, however: their mêlée attacks be indefinitely whiffed and they can still shoot you at point-black range!

Monsters can immediately attack after a pain frame

If you hit any monster (except the lost soul, which will always immediately stop moving), there's a chance that it gets stunned in pain. There's also a chance that it immediately retaliates with an attack after that (or the next time it sees you if it can't see you at the time), so think twice before you try to chainsaw through that pack of revenants. 💀

Revenants will not shoot fireballs in mêlée range

You can do the cha–cha–cha with some skeletons by always staying within their mêlée range and moving away right after you hear the punching noise. There's an intermediate area of 'chase range' where they will always try to walk up to you to enter the mêlée range (where they will always try to punch you instead). However, if you trigger their pain state, they can instantly shoot a fireball right in your face before you can even say super shotgun. 😿
Note: The retaliatory missile only gets shot in the chase range. You can delay it indefinitely if you stay in mêlée range.

Homing revenant fireballs have smoke tracers

Ever wondered how to distinguish between straight missiles and missiles? If you look carefully, you'll notice that homing missiles have a tail of smoke coming out of them!

Revenants are only as tall as imps

Now you know how the boneheads can fit in low corridors with their skulls clipping through the ceilings.

Attacks have knockback

All weapons, hitscan and projectile alike, knock back the actor on the recieving end proportional to the damage inflicted. In addition, if you're playing on Boom, the knockback can push actors off platforms as well!
The sole exception is the chainsaw. To make its latching ability to work, your attacks' knockback is disabled when you're holding the chainsaw. This means if you shoot a projectile and quickly switch to the chainsaw before the projectile hits its target, the target won't be pushed at all.

Archviles remember targets across teleports

Yep yep. It doesn't come up often but if you're fleeing from archviles into a teleporter right as their igniting you, their demon magics can fry your butt if the target teleporter is also in their range! 🔥 Since teleporting briefly freezes you, you're not gonna survive that!

Monsters will never change targets until their target dies or they get hurt

By default, monsters are either asleep, roaming (chasing after you) or focused on a target. Roaming or sleeping monsters will focus on a target right after they get hurt and won't switch targets until either the target dies or they get hurt by someone else (after the minimum number of steps they need to take).

Monsters need to move 100 steps after getting hurt to change targets

This is why you shouldn't shoot that cyberdemon that you want to infight with the barons. He's going to get mad at you and ignore the barons shooting him! Monsters don't have any focus by default and generally go after the you but if anything hurts them, they go after that target until they move exactly 100 steps (not necessarily away, just moving at all, so turret-positioned monsters will also switch targets), after which they stop being mad and return to the default state of casually going after you.
BUT!! archviles will instantly change target the moment they're hurt! They have no infighting threshold and they will forget the henchmen they're frying to get at you if your rocket splash burns them. This brings us to...

Archviles will continue to cast the same attack even after changing target

That's right! If you interrupt an archvile the moment he's about to zap some poor zombie, he will immediately turn his attention to you and finish the spell on you instead! That's why you should wait until he's done casting before shooting him.

Archvile attacks do splash damage that can be dampened by hugging a wall

Can't find a pillar to hide behind in time? No opportunity to shotgun him in hopes of triggering the pain state? I guess the only option you have is to... Hug a wall! That's right, some of the splash damage will happen behind the wall and hopefully you'll take only 20 damage from the hitscan attack alone.

First chaingun/pistol shot is guaranteed to be accurate

This is why chaingun is actually an excellent sniper gun! Just tap the trigger instead of holding it down and you'll be sniping those pesky hitscanners down their towers in no time. 😎

You don't have to be alive to trigger linedefs

That's right, this means your corpse can hit the level exit linedef and you can win the game after you die! You can use this to cheese some levels by strategically dying with some momentum to slide under objects you can't normally cross. 🪦

The first actor to damage a barrel provokes the ensuing infighting once the barrel explodes

Just because the projectiles won't hurt each other and they won't accidentally claw each other doesn't mean the Bruiser Brothers won't get in a feud! If someone damages a barrel, each monster that gets hurt once it explodes will get miffed at that monster (or you, if you're responsible).

Mancubus fireballs have a small chance of noclipping through walls

Mancubi can wallhaxx and occasionally shoot through walls. Make sure you aren't hiding behind thin walls when dodging their projectiles! This also applies to imp, hell knight and baron of hell fireballs as well, although to a much lesser degree.

Any object will stop a lost soul regardless of Z position

Even a shotgun lying on the floor will stop a charging lost soul no matter how high up! This also means that lost souls will hit whatever's beneath them whilst they're charging at you.

Lost souls can spawn inside walls after a pain elemental dies

Pain elemental's death explosion spawns lost souls, but if it dies too close to a wall, the lost souls can spawn in inaccessible places. Keep this in mind if you find yourself confused by zombieman sounds coming from outside the map!

Chainsaws will latch onto monsters during use

That's why that poor cacodemon you stunlocked can't move away from you. Be careful when playing with -fast monsters though, because the chainsaw's rate of fire can't keep up with those turbo pinkies that can bite you between the firing intervals and will maul you to pulp in no time! 🙀

Ranged monsters closer to you are more aggressive than farther ones

All (awake) monsters will constantly try to approach you, no matter where you are in the map, and they must at least move a bit before they can initiate an attack. Ranged monsters are increasingly more likely to shoot the closer they are to you. This is why, when tackling multiple stationary monsters, you should prioritise the ones closer to you.
Note: This does not apply to Nightmare! difficulty, where monsters constantly shoot at you for as long as you are in their lines of sight, but respawned monsters take longer to begin to shoot you to compensate for this.

Running against a wall builds up speed

You can use this to your advantage by running against a corner or a door to enter a room at full speed.

~Special moves~

Circlestrafing

This one's so simple that people almost always independently come up with it themselves in first-person shooters where you can strafe fast and dodge slow-moving projectiles. Strafing in a circle around large groups of monsters whilst shooting at them will

1. tightly confine them into the circle because they will keep trying to come towards you,
2. provoke infighting as the monsters in the back will accidentally shoot the ones in the front,
3. dodge projectiles because you keep moving away from incoming ones, and
4. keep you moving so you have constant access to pickups.

A lot of seemingly difficult fights can be reduced to 'circlestrafe to win' with some strategising.

Strafe running

As fast as the player already is, sometimes you need to be much faster, especially in order to jump over (run across?) wide gaps (in which case it's strafejumping without the jumping part). 🏃

• SR40: This is the most fundamental one, known since about a year after Doom came out. It becomes second nature for traversing long paths of land, much like Quake bunnyhopping, and helps you reach secrets. Basically, if you strafe left or right (40 units per tic) whilst running forwards (50 units per tic), you move faster diagonally, simply because you move in both directions at once at $\sqrt{{\mathrm{50}}^2+{\mathrm{40}}^2}=64$ units per tic towards the direction you're strafing at an $\arctan \frac{50}{40}\approx \mathrm{38,66}°$ angle. To give an example, if you turn left by about 38,66° (with your mouse, maybe), then hold down forward and right strafe at the same time, you will be moving straight ahead at $\frac{64}{50}=\mathrm{128\%}$ times your regular speed.
• SR50: This one was discovered much more recently. If you hold down the 'strafe on' key (the one that makes turn keys act as strafe keys, including your mouse movement), press a turn key to strafe and strafe in that direction with a strafe key, you will be moving at 50 units per tic instead of 40. Move forwards whilst pressing down this mess and you'll be moving at $\sqrt{{\mathrm{50}}^2+{\mathrm{50}}^2}\approx \mathrm{70,71}$ units per tic at an $\arctan \frac{50}{50}=45°$ angle towards your strafing direction. That's $\frac{\mathrm{70,71}}{50}\approx \mathrm{141\%}$ times your regular speed! Nyoooom~ In reality, SR50 is very rarely used outside speedrunning tricks involving short jumps because it's so unwieldly to press and you can't turn whilst using it (because your turn keys work as extra strafe keys now). I suggest assigning strafe-on to an unused mouse key.

Original Doom maps will never require you to straferun at any point (although custom maps may) and SR50 is rare enough that you won't ever need it outside speedrunning tricks.

Nukage rhythm

Let's see some facts!! 📠

• Fact #1: Nukage inflicts damage each tic.
• Fact #2: Your weapon bob is in sync with the game clock such that the weapon peaks on either side exactly at a tic.
• Conclusion: You can waltz with your weapon right before going onto damage floor and not take any damage in the nukage if you time your weapon's sway right.

This is why you shouldn't disable the weapon bob. A lot of in-game mechanics are tied to tics and your weapon bob is practically a clock.

Rocketjumping

This one is actually much rarer and harder to pull off than in Quake. Due to the lack of freelook, the only time you can footrocket is when autoaim scams you when you shoot at a monster below a ledge, and even then it's totally useless because you can't jump either way. But! you can run really fast and that means you can rocketrun even faster! Make sure you have enough health and armour, straferun in one direction, shoot your rocket at a wall to propel yourself in the opposite direction, then turn towards your destination. Remember: You can change direction and move (thus, straferun) midair.

Archvile jump

You know how each time an archvile zaps you you get blasted into the air? You can use this annoying oddity to your advantage by running in the direction you want to jump, timing the blast accurately and "jumping" onto otherwise unreachable platforms. Simple in principle, difficult in practice. You can get blasted way up in the air if several archviles zap you consecutively, letting you reach ridiculous heights (with invulnerability, of course).

Coöp jumping

Your attacks will push monsters a bit, and you can knock them off platforms by shooting them off the edge in Boom–compatible WADs. A consequence of this is that you can shotgun your coöp friends midair to push them further, to help them reach otherwise unreachable places.

Bumping

todo

Gliding

todo: easier on -shorttics

Wallrunning

todo: north, east

Fast switching

When you pick up a weapon for the first time and autoswitch to it, you can switch to a different weapon you already have in the middle of the switching animation to shave off a few seconds. This is especially useful with traps that abuse the autoswitch delay, such as a room that releases a horde of pinkies when you pick up the rocket launcher. Press 1 after your current weapon goes down and before the rocket launcher can appear in your hands, so you switch to fists/chainsaw instead.

Linedef skipping

todo

Peekaboo shooting

One of the most common tricks in Doom, which is intuitive enough for any new player to discover and internalise on their own, just like circlestrafing, is peekaboo shooting. Shoot monster, hide behind an obstacle to dodge their attack and reload your weapon, repeat. This works well with shotguns (reloading time + increased pain chance) and BFG (see 'streetsweeper' below), and is especially useful against hordes of zombies (who can be picked off before they start shooting), archviles (you eventually develop an intuitive sense of how long archvile's ignition attack takes to optimise this process) and pain elementals (who can be indefinitely prevented from shooting lost souls). Conversely, this doesn't work as well for cyberdemons and mancubi whose volley fire doesn't cease when you leave their line of sight.

BFG rush

BFG is, in essence, a super duper shotgun that happens to launch a powerful projectile and waits for it to land before spraying. Thus, it is the deadliest when fired up close. (I suggest installing a damage numbers mod to see where the tracers hit and how much damage each shot inflicts and experimenting to grok the tracer cone.) BFG rush is the art of 'cooking' the BFG projectile, running up to a cyberdemon or a spider mastermind and trying to land as many of the tracers as possible with a warm, green hug. Spider mastermind can be easily taken down with a single shot this way, sometimes before she can even react.
Cyberdemon, however, is the only monster in the game that can endure a max damage BFG shot and the common tactic to take him down is prefiring a BFG ball after he starts shooting, zigzagging through the volley and landing the shot at mêlée range before swiftly retreating for the next round. If everything goes well, he can be taken down in exactly two shots. The most important point is that you must approach him after he's already begun shooting at you, so that you know exactly when and where the rockets are fired in the process. Alternatively, simply distract him with infighting and BFG blast his butt before he's done killing his new target.

Streetsweeper

Sometimes you just don't care about BFG's projectile. It's a nice bonus when you fire it up close, but from a range, it significantly delays the tracers, limiting its usefulness when a pack of revenants is about to corner you. A common tactic is to sacrifice the projectile altogether and peekaboo shoot (see above) with the super duper shotgun only. Hide behind a wall, set your angle to face the monsters, fire at the wall and immediately strafe out of your cover to blast whatever's standing in front of you with the tracers. (There's about half a second of delay between the projectile's impact and the tracers' firing.) It is imperative that the projectile hit the wall before you peek out or you'll have to wait until the it hits something before shooting the tracers.

BFG stacking

There's no kill like overkill! This tactic works under very specific slaughter map conditions with lots of open space and tightly packed groups of heavy monsters being released in waves. You need to prefire your BFG towards where the cloud of cacodemons or party of archviles (or any other group of strong monsters) is about to be let loose into the arena, and simultaneously run to that point. But don't stop shooting once the projectile leaves the gun. Keep running and shooting all the way until you're there. If everything goes well, you will be running behind a tightly stacked chain of projectiles (owing to the Doppler effect), none of them having landed yet. If you time it well, all of them will land on the first row of monsters in quick succession, turning your BFG into a super duper automatic shotgun, with rapid-fire cones melting through hordes. This trick can also be used with the rocket launcher, to a lesser extent.

Advice for n00bz

• There's no 'correct' way to play Doom. There's no 'correct' difficulty level either. Ignore the haters and feel free to skip tough maps, read walkthroughs and enable crouching/jumping/freelook (even if the mapmaker tells you not to). Play with cheats, helper mods, overpowered weapon mods (like the infamous Brutal Doom) and lots of saves if you find it fun. The main objective in Doom is to have fun. 😺
• If you get stuck, go check out Doom Wiki. In fact, check it out even if you aren't stuck because it's choke full of useful info. Doomworld forums are also very good. Check out their Cacowards for crème de la crème WADs. I also strongly recommend Doom2.net for all sorts of information.
• Most maps will assume a 'pistol start' 🔫, so you don't need to worry about pickups if you're just jumping into a map with idclev. In fact, most custom maps will assume this is what you're doing, making continuous playthrough easier.
• Practice makes perfect. If you can't beat a fight or a map, just keep trying (perhaps on a lower difficulty). You'll improve a bit with every attempt. But don't push yourself too much and know when to take a break.
• Maths problems and Doom combat puzzles have one thing in common: Your task is reducing the complex problem at hand into a simple one you know how to solve. When tackling a combat puzzle, spot complicating elements and prioritise them. Once they're eliminated, approach the rest as normal. Most arena fights can be reduced to 'circlestrafe to win'.
• Always be on the move! Don't sit around like a sitting duck who sits around or you'll catch projectiles! (Just make sure you know where you're going.) Doomguy's biggest strength is being able to run at inhuman speeds. Run, run, run! Leave the 'always run' option on at all times and only use walking for aligning yourself on catwalks and tiny platforms.
• Don't mute the game! Sound cues are super important!
• Don't rush but don't linger either; the less time you spend in combat, the less likely you are to die.
• Super shotgun is your bread and butter in Doom II. Everything else is a sidearm. Super shotty will send the cyberdemon back to heck, mow through chaingunners and turn pinkies into goop. The super shotgun is ~2–3× more effective than rocket launcher against monsters immune to splash damage.
• Try to line up monsters so that they are more inclined to infight, their attacks can't reach you and your hitscan attacks are more efficient.
• Rely on infighting to save ammo and reduce your load. Cyberdemons will draw fire and clear hordes for you — just watch out for stray rockets! But...
• Infighting is useful and fun but it also complicates things, so know when to resort to it. You can always assume awake monsters are always moving towards you and trying to shoot at you — unless they're infighting. If you can easily beat a fight without infighting, do so.
• When triggering an infight between a strong, durable monster (eg a cyberdemon) and softer monsters (eg hell knights) that it would easily beat, make sure to hurt the former before the latter can, so that it will be too busy chasing you down to notice it's getting torn apart by other monsters.
• When two monsters are infighting, help the one you think would lose, so that the winner will be on the verge of death by the time their duel is over.
• Try to avoid changing targets midcombat as much as possible. Being surrounded by several wounded monsters is not preferable over few monsters at full health.
• Use the chaingun to stunlock monsters with high pain chance, such as lost souls. Don't give them a chance to even attack you.
• Don't underestimate low-tier monsters like lost souls and hitscanners. The more you neglect them, the more chip damage you will accumulate and deplete your health before you realise.
• Keep a close eye on your health and armour and know when to go back to search for leftover medikits, especially before big fights.
• Prioritise picking up items in rooms you don't expect to return and try to leave behind items (especially medikits) in rooms you know you're going to return for another fight.
• When shooting rockets into a group of monsters, aim at the middle to maximise splash damage.
• Don't approach cyberdemons in straight lines. Cyberdemon shoots three rockets per attack and you can easily come close to him with a precise zig-zag movement. You will eat a rocket to your face if you run straight up to him.
• Don't stand close to walls or columns when fighting a cyberdemon or you'll take splash damage off every rocket you dodge. In addition, don't give cyberdemons the high ground either because the rockets you dodge won't swish past you but directly hit the ground next to you and the splash damage will burn your butt!
• When taking on multiple cyberdemons, herd them into a tight group so that you can keep them all in your field of view. It's always a bad idea to turn your back to a cyberdemon, especially when you're fighting another one!
• If you're at risk of getting flanked, don't stand in the middle. Instead, try to stand close to one edge of the room to kite monsters in that direction. This will leave a corridor you can rush through if you need to beat a hasty retreat.
• In a large arena fight with little space to move around, keep track of the monsters you've damaged in the crowd and try to take them out before focusing on others. Spreading your damage will only lead to your getting overrun by the horde.
• Always be careful shooting rockets when there are pinkies roaming around or towards pain elementals and lost souls, and don't shoot rockets in the direction you're running towards if there's a chance a monster can run into you from a side, or you'll be facerocketing yourself.
• The plasma gun is your panic button. If you find yourself surrounded by pinkies, cacodemons or revenants, reach for the plasma gun to quickly open a way out.
• Lure dangerous monsters away from where archviles will spawn before killing them. Alternatively, if the archviles are too much for you to deal with, you can strategically kill low-tier monsters to use their corpses as distractions instead. They'll be too busy resurrecting small fry to focus on zapping you. ⚡
  You can also pick certain monsters like mancubi as resurrection bait. Mancubi are slow and occupy a lot of space and will slow down archviles' movement in narrow spaces.
• Partial invisibility is good against hitscanners but terrible against projectile hurling monsters. Projectiles will get highly unpredictable and your dodging skills will fail you with partial invisibility. It will still help you in situations where you need to stand still, especially if you're far away from the monsters.
• Learn to recognise combat puzzles based on monster attributes and intricacies. Mapmakers will give you specific pickups and pit you against different groupings of monsters with creative map features. You'll get to grok the patterns in these puzzles with practice.
• Grok monster properties: attack times, movement patterns, stun chance, sounds, hitpoints, attack damage (minimum, maximum and average), and your own weapons' damage. For example, know how many super shotty shots (say that ten times fast :-3) it takes to take down a baron of hell on average, recognise the sound a cacodemon infighting multiple pinkies makes and so on.
• Slaughter maps are all about crowd control, swift manoeuvring, situational awareness, finessing of area denial, and clever management of priorities, time and resources, rather than simply killing lots of monsters at once. Stay calm, try again and again, come up with new tactics on the fly. It all comes with practice.
• Most assumptions about priorities go out of the window once you start playing on Nightmare! difficulty. Always stay on the run and don't waste your precious ammo to kill monsters that aren't immediately dangerous. The more time you waste killing windowdressers, the more monsters will have the time to respawn. It's better to damage monsters strategically so that you can kill them easily when you have to.
  Note: Keep in mind that corpseless monsters like pain elementals don't respawn, so they're free game.
• Save often if you don't want to repeat the whole map. Use the opportunity to explore before going for a single-segment run. 😉
• Ignore all this advice if you have a good plan in mind. Adapt to changing circumstances.
• And most importantly, don't forget to have lots of fun! There's no point in playing if you aren't having fun!

Tactics and tricks~!

More specific advice

• Move in quick, narrow circles to dodge projectiles in cramped spaces. You can sit still and only move to dodge projectiles this way to take no damage at all.
• Whilst being chased by a revenant missile, make a move towards a wall rather than away from it. You can combine this with the trick above to make circles towards the wall to clear incoming missiles.
• Sharp turns across corners will help get homing missiles off your tail. If you want them to follow you to cause infighting, manoeuvre with gentle curves out in the open to establish a revball trajectory.
• Move back and forth in a broad horseshoe shape when dealing with a large revenant horde to accummulate homing missiles and get rid of them on each end. (Do not turn before the revball is completely gone.) This works even better with groups of meat shield monsters. Note that this works only in large rooms. In narrow corridors, use the above tactics as normal instead.
• When dealing with two revenants, keep one in chase range as you deal with the other. It's much easier to whiff punches than keep track of homing fireballs from two targets.
• When circlestrafing a mixed group of monsters to get them to kill each other, prioritise killing revenants. Revenants are fast and can walk out of the circle of control faster than the others. Not to mention the homing missiles that accumulate behind you will take you out if you get stuck anywhere.
• Dodge left when a mancubus first shoots. The mancubus shoots from his front (towards the target) whilst shooting at his left (the target's right) at first, then his right (the target's left). On the third volley, he shoots both left and right but not the middle. Additionally, the angle between his left and middle attacks is narrower than the one between right and middle, meaning you get more leeway to move if you dodge left.
• For the same reason, when circlestrafing around groups of mancubi, do so in an anticlockwise manner. They won't be able to keep up with you as they shoot behind you.
• When dealing with a massive horde of revenants in a large arena, perform the butterfly manoeuvre. Kite the horde towards a corner of the room to make space on the opposing corner, make a U shape around the monsters to the next corner next to you, make a little loop at the corner to get rid of the homing missiles. Retrace the U shape back to the starting corner and do another loop there. Repeat, trimming the horde and clearing your path with your BFG the whole time. Keep going until the problem is reduced to 'circlestrafe to win'. Until then, if you stop, you die.
• Due to an infamous bug, hitscan attacks can harmlessly go through an actor if its hitbox is located in more than one blockmap. This is normally unnoticeable outside certain map features like corridors that directly cross the boundary between rows of blockmaps. Enable the blockmap grid in the automap and shoot diagonally to the grid lines to make sure your shots land.
• Hide from monsters if you want to lure them somewhere. Awake monsters always know where you are at all times and will try to approach you. By entering a ranged monster's line of sight, you're giving them the option of shooting you instead of moving towards you. They will opt to shoot more often, the closer they get to you and that will delay their arrival.
• If there are pain elementals amongst the monsters that flow in when you initiate a fight, hurt them first. This gives you time to square off before taking them down. Otherwise, they will almost certainly start infighting and fill the arena with lost souls before you can get to them.
• If you take on an archvile with a plasma gun and successfully trigger the pain state, you can rest easy that he's dead soon. He will never have the time to recover from the pain state and start zapping you before he dies, thanks to the plasma gun's high rate of damage per second.
• When dealing with a free-roaming archvile, run up to him in between zaps to keep him stationary where he can't revive corpses or walk past your cover.
• When playing on Nightmare! difficulty, soften monsters standing at strategic positions you're going to return to (such as teleporter endpoints), instead of killing them outright, so that you can one-shot them upon your return.
• On Nightmare! difficulty, if a monster was targeting the player before it died, it will respawn targeting the player. Otherwise, it will wake up idle. You can rely on infighting to reduce the number of monsters chasing you through the level.
• Hugged pain elementals can be used for pushing the player in very small amounts to trigger tiny linedefs (like the broken secret of M15 in Doom II).
• Once you grok the delay between shots when continuously firing the shotgun, the super shotgun or the rocket launcher, you can hold down the attack button and time your aim to maximise your rate of fire.
• If you have your back to the wall trying to curb a river of hell nobles flowing in, stay just out of splash damage range as you pump rockets into the crowd. The closer you stay to them, the more they will stop to hurl fireballs at you rather than try to move closer to you, thus slowing them down and saving you time.
• When you're using a tanky monster for infighting (such a cyberdemon), hurt it and stay in its line of sight for as long as possible (and make sure the collateral damage hits other monsters). As long as it sees you, it will try to shoot you instead of walking towards you (which would eventually reset its target), so it won't fight back against the monsters that are mauling it to death. This is more effective with fast monsters.
• What weapon to use to trigger the pain state?

  For monsters with low pain chance

  • Double shotgun: As each pellet is checked individually, a single SSG blast will cause the pain chance to be calculated 20× (assuming all pellets hit). This makes SSG an excellent weapon against archviles and cyberdemons if you're mobile enough to evade the attacks between blasts.
  • Chaingun: The chaingun is your last resort for triggering the pain state, as a rapid rate of fire is all it has, but by gods, it sure has one.

  For monsters with high pain chance

  • Chainsaw: You can cut through arachnotrons and pinkies like butter with your trusty chainsaw (and cacodemons and pain elementals if you can reach them), but beware that the chainsaw is a bit buggy in more vanilla source ports and should be outright avoided with -fast monsters.
  • Chaingun: The chaingun is an excellent choice for stunlocking monsters with high pain chance and even hunting revenants from a distance where you can avoid their retaliatory missiles. Nevertheless, it's an expensive solution as your bullet supply would melt away after a few mid-tier monsters.
  • Shotgun: The ol' reliable shotgun is your last resort with seven pellets a blast and should be preferred over super shotgun due to its faster rate of fire. If you can dodge the attacks between each fire, you're guaranteed to easily take the monster down with a lovely waltz.

Fun facts! 😸

Prepare to get your socks knocked right off because these facts are fun (and too nerdy to be in the essentials section)!! (Again, many thanks to decino and Coincident! In addition, check out Colin Phipps's Classic Doom Curiosities.)

• Horizontal autoaim tries the angles 0°, 6,5°, -6,5° (in that order) for your projectiles (ie rockets, plasma balls and BFG balls).
• Projectiles and lost souls travel the same horizontal distance at the same speed, regardless of the vertical difference. Thus, ascending or descending projectiles will be faster.
• Idle monsters can be damaged on every second idle frame without waking up if they can't hear your gunshots, unless the damage triggers the pain frame.
• Blockmap bug: Hitscan attacks and projectiles will miss an actor even if they pass through its hitbox, as long as they only pass through blockmaps that don't contain the actor's centre point. Enable block boundaries in the automap to see if the monster you just shot through is standing on one.
• A spiderdemon (or an arachnotron) can get paralysed if, before she wakes up for the first time, an actor clips into her massive bounding box, which is possible when it overflows into neighbouring blocks, as only the blockmap containing her point of origin is checked for collisions. This can be done with mancubi as well, but they are much less likely to be placed on the edge of a blockmap.
• Splash damage hurts a given monster as many times as the number of idle monsters in the same blockmap that take damage and wake up but don't go into pain state. (That's quite a mouthful!)
• It's possible to die to a telefrag. If you telefrag a cyberdemon the instant he fires a rocket (before it leaves his collision box), it will explode inside you.
• The archvile won't initiate an attack past 1088 units unless he goes into the pain state, in which case his next attack has an infinite range. This can happen when he kills another monster he's infighting and hurts himself with the splash damage of his own attack, so he can target you from far away out of the blue.
• The revenant hitbox 'jumps' (by 16 units) when shooting. All monsters shoot from the centre of their hitboxes. Since the revenant is technically as tall as an imp despite its longer sprite, the hitbox moves up for the tic the revenant shoots so that it doesn't shoot out of its crotch. An implication of this is that if you time your shot right, you can push a revenant onto a platform (on Boom), although it will climb down since monsters can climb across platforms with up to 24 units of height difference.
• Projectiles can climb stairs with steps at most 24 units high.
• Hitscan attacks only travel up to a certain range.
  • BFG tracers: 1024
  • Bullets: 2048
  • Fists: 32
  • Chainsaw: 33
• Remember ghost monsters? All monsters in the map (including you!) turn to ghosts if a hitscan attack you shoot goes over too many (128) linedefs and objects. Exceedingly rare but super annoying! You can't even trigger linedefs (but still trigger damaging floor death exits).
• -shorttics: Recording a demo (at least in the original format) will lead to a loss in precision when turning with mouse. Specifically, your turning movement is limited to multiples of $\frac{360°}{2^8}\approx \mathrm{1,4063}°$ ("short tics") rather than the usual $\frac{360°}{2^{16}}\approx \mathrm{0,0055}°$ ("long tics"). A caveat is that a successfully landed punch or chainsaw hit will internally change the player's internal angle by a small amount. Long tics are precise enough for this not to be a problem, but with large turning steps of short tics, you're always stuck with a tiny offset that makes gliding impossible.
• The rocket the player shoots passes through their hitbox harmlessly if they manage to catch up with it (eg teleporting, wallrunning). This is similar to how revenants will block other revenants' missiles but not their own. However, if the player dies and respawns, in a deathmatch for example, and manages to catch to the rocket they shot in their previous life, the rocket will successfully explode on them because respawning creates a new entity each time and the rocket does not update its shooter's information across deaths.
• Dead players can still shoot BFG tracers out of their corpses once the BFG ball they fired whilst they were alive lands.
• Both the rocket launcher and the BFG have a short period between when the trigger is pulled and when the projectile is launched. This can be used for pulling the trigger before, say, taking a teleporter and shooting 'silently' from the exit teleporter. The plasma gun is the only projectile weapon that fires instantly.
• Certain linedefs can be triggered by barrels, spawn cubes and specific projectiles, namely those of mancubi, revenants and arachnotrons.