DOOM has a lot of terminology associated with it. Following is a list of external terms and their definitions, sorted relationally:
WAD: DOOM resource file. Stands for “Where’s All The Data?”.
IWAD: Internal WAD. A primary game; required for play.
PWAD: Patch WAD. A secondary data file, which inherits from and overrides an IWAD.
In modern times, a PWAD may be packaged as a pk3 archive instead of multiple WADs; these can be treated simply as WAD files for most practical purposes.
DEH: DeHackEd file; provides patches to the Doom engine to override default strings or alter behaviours. Several ports will auto-load these as appropriate if they’re in the same directory as the WAD. Largely deprecated in recent times in favor of port-specific scripting engines such as Decorate.
Port: Strictly speaking, any Doom engine that isn’t the original DOS executable. Also used in the idgames database of Doom modifications to refer to maps that require a limit-removing or enhanced port of Doom, with Boom, GZDoom, and Zandronum being the de-facto standards. Chocolate Doom holds somewhat of a middle ground, being technically a port, but one that attempts to be bug-for-bug compatible with the original Doom executable while offering a handful of minor enhancements.
Vanilla: A map set which works without modification in the original Doom executables. Also refers to gameplay styles which are similar to the original Doom, not taking advantage of port features or scripting.
Episode replacement: A map set which replaces most or all of an episode (generally 8 or 9 levels).
Megawad: A map set which replaces 15 or more levels in the respective IWAD, but most typically all of them (up to 36 for Doom, up to 32 for Doom 2), or more rarely, even more.
Slaughtermap: A style of map where the challenge primarily comes from facing gigantic hordes of enemies.
Pistol start: Beginning a map with no prior resources from previous maps. Occurs normally during gameplay if the player dies and doesn’t reload a previous save. Can be induced by a map author under certain circumstances.
Deathmatch: Player-versus-player gameplay.
Frag: Scoring a kill against another player in Deathmatch.
Gib: Blowing weaker enemies to bits. Accomplished by dealing more than double the damage needed to defeat it; specifically, the final source of damage must deal enough damage to reduce the current HP to less than the negative of its starting HP. Only (former) humans and imps can be gibbed (as other enemy types lack the necessary animation frames), and not, in practicality, by hitscan weapons (except the Berserk Fist) due to either being too weak (like the pistol) or relying on multiple sources of damage (like the shotgun).
Circle-strafing: Running in circles around one or more opponents by combining normal movement with strafing.
Strafe-running: Running diagonally by combining normal movement with strafing. Notable because of how Doom physics work, resulting in a net increase in speed versus running or strafing alone.
SR50: Strafe-running using both the dedicated strafing keys + the strafe-lock key combined with forward movement (4 keys in total). Named due to the fact that it sets both horizontal and vertical speeds to 50, 10% faster than the normal diagonal movement cap of 40%. Extremely difficult to pull off usefully, as moving in this way makes steering impossible.
Rocket jumping: Gaining vertical and horizontal momentum by taking advantage of an explosion, typically from a rocket fired at point-blank range.
Suicide exit: A method of exiting a level, typically prematurely, by taking advantage of momentum exhibited by corpses alongside a type of level exit which is effectively a hole in the ground. Given enough force upon death, a player’s corpse will slide a fair distance, and given that the height is set to floor level to give the appearance of falling over, it is possible to slide underneath certain obstacles and into the exit hole, completing the level and beginning the next with a pistol start.
Pain chance: The relative chance for a monster to skip their attack and movement animations due to being hit with a weapon. Generally, the stronger the enemy the smaller the pain chance, but overwhelming firepower has the potential to make any enemy flinch.
IWAD differences
The two most-used IWADs are DOOM.WAD and DOOM2.WAD, with DOOM2.WAD being the most popular. There are also TNT.WAD and PLUTONIA.WAD (Final DOOM), but the gameplay elements remain unchanged and they are almost-compatible drop-in replacements for DOOM2.WAD, the primary difference in that case being the textures and intermission texts. Similarly, FREEDOOM1.WAD and FREEDOOM2.WAD are Free Content replacements for the commercial IWADs that are fully legal to freely distribute (though the graphics are near-universally regarded as terrible).
The major differences between the two IWADs are as follows:
Episode structure
Doom uses an episodic format, so levels are named accordingly, e.g. E1M1.
Doom 2 eschews the episodic format in favor of sequential levels, e.g. MAP01.
To achieve a similar effect, you’ll find that some map sets, such as Scythe 2, will kill the Player at the end of select maps and then end the map, forcing a pistol start on the next map.
Doom Megawads typically follow a similar structure to Doom: 4 episodes consisting of 8 regular maps and 1 secret map.
Doom 2 Megawads typically follow a similar structure to Doom 2: 30 regular maps and 2 secret maps.
Intermission screen
Doom and Doom II both show a statistics screen at the end of each level, tallying up the percentage of kills, secrets found, items collected (not including radsuits, medikits or green/blue armor pickups), time taken to complete the level, and the par time for the level (purely for the sake of personal challenge, and usually ignored/unaltered in PWADs).
It is possible to get more than 100% kills due to enemies being resurrected or to new enemies being introduced in other fashions.
Depending on the port, it can be possible for any of the statistics to be either 0% or 100% if nothing of that category is present on the map. For instance, on maps with no secrets, some ports will claim 0% of the secrets were found, and others will say 100% of the secrets were found.
The background graphic in Doom’s first three episodes depicts the player’s progress across a map of the area the episode takes place in. The fourth episode, as well as Doom II, simply shows a static background image.
Each Doom episode ends with a text screen and some artwork. Doom II, not having an episodic format, omits the art but does still have text screens after certain maps. Player-made Megawads typically contain these as well.
Weapon selection
DOOM features 8 weapons, balanced relative to each other. Weapons come in two types: projectile (launches something which can be potentially dodged) and hitscan (fires immediately with no visible projectile). All weapons work off of a dice pool instead of direct damage values, allowing for some minor variation in damage output. They are as follows:
Fist: Unarmed attack, normally used only when all other ammo is depleted. Does damage comparable to the pistol. When under the influence of the Berserk Pack, can do damage comparable to a rocket launcher. Technically hitscan, fired early in the animation and with a range limit.
Chainsaw: Occupies the same slot as the fist and does rapid-fire melee damage, tending to “lock” the player to the monster. Situationally useful, but unaffected by Berserk. Technically hitscan, but with a range limit.
Pistol: Starting pea-shooter. Slow rate of fire, but the first shot is always perfectly accurate. Uses bullet ammo. Hitscan.
Shotgun: Shoots seven pellets in a horizontal line. Most effective at short to mid-range, but can serve as a reasonable sniping weapon. Uses shell ammo, and is balanced by a reload animation after each shot. Hitscan.
Chaingun: Generally considered an upgrade to the pistol. Fires moderately rapidly with no spin-up, cool-down, or reloads needed. Uses the same ammo pool as the pistol and does the same damage per shot, but loses considerable accuracy after the first shot. Fires at least two shots per burst if at all possible. Hitscan.
Rocket launcher: Fires powerful, somewhat slow-moving rockets at a moderate pace. Extremely dangerous in close quarters due to splash damage. Uses rocket ammo. Projectile. If the fire button is being held down as it is switched to, it will be necessary to release the fire button first before firing will be allowed, as a safety feature.
Plasma rifle: Fires moderately powerful plasma balls extremely rapidly and with a very loud sound effect. While burst fire is useful to conserve ammunition, there is a delay upon releasing the trigger before firing is allowed again. Uses plasma cells as ammo. Projectile.
BFG 9000: After a short delay, fires a large plasma ball; approximately half a second after it detonates, 40 invisible hitmarkers are released in a cone-shaped arc from the player in the direction the ball was fired, doing additional damage. Does devastating damage to a single target, especially at point-blank, and can easily take out rooms of lesser hellspawn in a couple of shots. Shares ammo with the plasma rifle, but takes 40 cells per shot. Due to its unusual behaviour and staggered firing sequence, practice is required, especially for deathmatch use. Hybrid projectile and hitscan. If the fire button is being held down as it is switched to, it will be necessary to release the fire button first before firing will be allowed, as a safety feature, albeit more for your stock of ammo than yourself.
Doom 2 changes the make-up a bit by introducing one more weapon:
Super Shotgun (SSG): Shares a slot with the shotgun, but fires twenty pellets in a large conical pattern, including vertically, using two shells per shot. Has a reload animation twice as long as the shotgun’s. At point-blank, the damage regularly exceeds the rocket launcher, being roughly three times the power of the standard shotgun, and it is commonly used in clearing rooms of minor enemies. Hitscan.
Monsters
Doom 1 has a fairly extensive bestiary, presented here by category:
Doom
Former Humans
Zombieman (aka ‘trooper’): A human possessed by demonic entities. Walks in a zig-zag pattern and fires occasional rifle shots, similar to the player’s pistol but slightly weaker. Drops bullet clips when killed.
Shotgun guy (aka ‘sergeant’): Another possessed human, this time with black armor. Walks in a zig-zag pattern and fires a slightly weaker 3-pellet shotgun. Somewhat more HP than the zombieman. Drops a shotgun when killed.
Hellspawn
Imp: A brown spiky humanoid. Has a melee attack and a projectile attack in the form of a moderately-speedy fireball. Twice the health of a sergeant.
Demon (aka ‘pinky’ or ‘pig’): A bull-headed monster that can only attack in melee range, but has a very strong bite. A bit of a bullet sponge, having 5x the HP of a sergeant. Moves very quickly in a zig-zag pattern.
Spectre: Exactly the same as a demon, but partially invisible. Often placed in dark rooms or used for flanking attacks.
Baron of Hell: Large pink satyr-like creatures. Third-highest HP in the game at nearly 10x that of the demon. Has both a melee attack and a projectile attack with huge damage potential.
Cacodemon: A large spherical monster crowned with horns. Has both a melee and projectile attack and is able to float wherever it pleases. Almost 4 times as much health as a demon and hits hard, but a lot slower and quick to flinch.
Lost Soul: Flaming skulls that swiftly charge at their prey. Not quite as tough as a demon, but very persistent and able to fly. Additionally, they’re completely silent until they attack. Will flinch after any attack.
Bosses
Cyberdemon: A missile-launching skyscraper with goat legs. 4x the health of a Baron and entirely immune to splash damage. Has only a projectile attack in which it shoots a barrage of 3 rockets identical to the player’s.
Spider Mastermind: A giant brain riding a spider-like chassis with a massive chaingun attached. Almost as much HP as a Cyberdemon and a powerful hit-scan projectile attack that fires three shots at a time at a rate of 425 per minute. Like the Cyberdemon, it is also immune to splash damage.
Doom 2 expands the bestiary a fair amount, as follows:
Doom II
Former Humans
Heavy weapon dude (aka ‘commando’ or ‘chaingunner’): The strongest possessed human, clad in red. Fires a chaingun that is slightly weaker and slower than the player’s, which they drop upon death. Has more than twice the HP of a Sergeant. Often used as an incredibly annoying sniper.
SS Trooper: Only shows up in the secret levels. Imported from Wolfenstein 3D. Dressed in blue and fires a rifle in a similar fashion to the chaingunner, though less rapidly. Has a little less than twice the HP of a Sergeant.
Commander Keen: Only shows up in the second secret level. Harmless and easy to kill.
Hellspawn
Revenant: Tall, fast skeleton with rocket launchers. Has a powerful melee attack as well as two types of rockets, one of which is homing, distinguishable by the grey smoke trail. Will often fire a non-homing rocket in retaliation for being hit. Somewhat less HP than a Cacodemon.
Mancubus: A large, slow, brown lumpy monster with flame-launchers for arms. Fires in three angled waves with massive damage potential. Twice the HP of a Revenant.
Hell Knight: Essentially a variant of the Baron of Hell with half the HP. Looks identical aside from its tan skin.
Arachnotron: A smaller variant of the Spider Mastermind, but with blue eyes and a plasma rifle which fires at about 1/3 of the rate of the player’s. Same amount of HP as a Hell Knight.
Pain Elemental: A floating brown monster with no direct attack. Fires Lost Souls out of its mouth, and several explode out of its body on death. Slightly less HP than the Hell Knight. Vanilla Doom has a limit on the number of currently spawned Lost Souls to avoid completely overwhelming the player (and the player’s computer); if this limit is hit, this monster is unable to attack at all.
Archvile: A tall, tan, alien-looking monster. One of the most dangerous creatures in the game. Has both a devastating magic attack which can only be avoided by blocking the line of sight as well as the ability to resurrect any enemy that leaves a corpse, with the exception of boss monsters and other Archviles. Somewhat more HP than the Mancubus.
Bosses
Icon of Sin: Only shows up in the final level. Structurally, it’s made up of several parts: the wall decorations, a monster-cube spawner, and a weak point. Can summon any hellspawn, and does so with regularity. Can only be damaged by rockets in the vanilla game, barring exploits.
Items
Items are all the same in both titles with the exception of the addition of the Megasphere in Doom 2, and can be roughly broken down into health, armor, and utility categories, with two cross-overs.
Health
The player starts the game at 100% health. Some healing items can increase this to a maximum of 200%.
Health bonus: A blue vial of liquid. Grants up to 1 HP, but cannot exceed 200.
Stimpack: A small first-aid kit. Grants up to 10 HP but cannot exceed 100.
Medikit: A large first-aid kit. Grants up to 25 HP but cannot exceed 100.
Soulsphere: A blue sphere containing a human soul. Grants up to 100 HP, but cannot exceed 200.
Armor
The player starts the game at 0% armor, with the category defaulting to green security armor, which absorbs 1/3 of all damage. This category can be altered to blue combat armor if said armor is acquired, which then absorbs 1/2 of all damage. The category will stay on combat armor until another full set of security armor is picked up. Like Health, armor maxes out at 200%. Absorbed damage is deducted from the remaining armor points; as a consequence, combat armor degrades more quickly than security armor.
Armor bonus: A brown helmet with a green glow. Grants up to 1 AP, but cannot exceed 200.
Security armor: A green breastplate. Sets armor to 100 and changes the category to security armor. Cannot be picked up until/unless the player’s armor percentage is less than 100.
Combat armor (aka ‘megaarmor’): A blue breastplate. Sets armor to 200 and changes the category to combat armor.
Utility
Ammo: Bullets come in clips (10) or boxes (50), shotgun shells in bunches (4) or boxes (20), rockets singularly (1) or in boxes (5), and cells in small batteries (20) and large batteries (100). Previously unowned weapons picked up will grant twice the ammo of the small pick-up of its type. For enemies that drop ammo types (including guns), the ammo you get from those pick-ups will be halved relative to its small pick-up size since the enemy presumably used the rest up. There is a limit to the amount of ammo the player can carry, as follows:
200 bullets
50 shells
50 rockets
300 cells
Backpack: A brown backpack. Grants one small pick-up’s worth of each ammo type. The first one found permanently doubles ammo capacity until the end of the episode (Doom) or game (Doom 2), provided the player isn’t killed.
Computer Area Map: A small green computer. Shows the full map of the level on the Automap, with certain exceptions as designated by the map author.
Invulnerability Artifact: A green sphere containing a powerful spirit. Grants (almost) complete invulnerability for 30 seconds, during which the player’s vision is radically altered.
Keys: Six variants that come in two types (keycard and skull) and three colors (red, blue, and yellow). Opens corresponding doors. Relinquished upon exiting the level.
Light amplification visor: Big goggles. Grants enhanced lighting. Wears off after 120 seconds.
Partial invisibility: A red and blue sphere. Grants partial invisibility, much like a spectre, for 60 seconds. Can be dangerous, as it causes enemies to aim wildly once the player is detected.
Radiation shielding suit (aka ‘radsuit’): A white suit that protects from irradiated floors. Wears off after 60 seconds. Causes a green fog while active.
Cross-overs
Berserk Pack: Combination health and utility item. A black first-aid kit. Grants up to 99 HP but cannot exceed 100. Grants berserk status for the duration of the level (despite the visual effect suggesting otherwise), altering the fist to have damage mechanics similar to a rocket, sans splash damage.
Megasphere (aka ‘supercharge’): Combination health and armor item. Introduced in Doom II. A tan sphere containing a hellspawn’s soul. Changes the armor category to combat armor and grants up to 199 HP and 200 AP but cannot exceed 200 in either category.
Terrain features
The Doom terrain itself can be deadly, and it can also be used as part of a puzzle. Some notable features:
Irradiated ground: Some parts of the ground, usually covered in green slime or red lava, are irradiated or otherwise damaging and will damage the player on a regular basis unless protected by a radsuit or invulnerability sphere. There are several variants, and the very most damaging floors have a 1/64 chance per second to damage the player even through a radsuit.
Barrels: Your best friend or worst nightmare, depending on how you use them. All barrels are explosive and contain irradiated liquids. Great for setting off chain reactions.
Crushing ceiling: The player can potentially survive this, but it will hurt massively. Sometimes used as a sudden trap. Enemies killed this way (or who have a door closed on their corpse) will become crushed gibs and ineligible for Archvile resurrection. Crushing ceilings will also destroy enemy projectiles as well as any ammo or weapons they drop.
Doors: Doors are usually readily apparent. Many hidden doors look like regular walls, however. Many doors require a key or switch, and some can be activated by shooting them or triggering a pressure plate. In vanilla Doom, doors always open vertically. Although fairly rare, it is possible to make a door one-way and/or usable only once.
Switches: Switches can look like a computer monitor, a large toggle switch, a green light, or a red and green unit with a small switch. These usually open doors or lower barriers. Occasionally requires a key. Some switches can also be activated by shooting them.
Monster closets: Used heavily in Doom 2, sometimes walls will burst open and monsters will swarm into the room. A variant of this is the “instant elevator” which makes an enemy pop up from the floor.
Pressure plates: Pressure plates can be anywhere and are invisible. Often used for activating lifts and secret doors.
Lifts: Lifts can usually be activated simply by pressing the “use” key next to them. Sometimes there’s an actual switch or a pressure plate nearby. Although very rare, it is possible to make a lift one-way and/or usable only once.
Teleporters: Often red with a demonic drawing on it, though silver versions exist and often denote an exit or something special, it is entirely possible for it to be unmarked. Upon being stepped on, teleports both players and monsters to a pre-determined location, providing it’s not being used as a level exit. Often one-way.
Difficulty levels
The biggest decision you make will be the selection of difficulty levels, of which DOOM has 5. Difficulty levels affect, based on the map’s design, the placement (or even occurrence) of monsters and items, as well as a few other details:
+--------------------+----------------------------+---------+---------------------------------------+
|Skill name |Thing placement |Ammo/Unit|Special |
+--------------------+----------------------------+---------+---------------------------------------+
|I'm too young to die|The same as in HNTR |Double |Players take half normal damage |
|Hey, not too rough |Least numbers or strength |Normal |N/A |
|Hurt me plenty |Default numbers or strength |Normal |Used by default |
|Ultra-Violence |Greatest numbers or strength|Normal |The only acceptable difficulty |
|Nightmare! |The same as in UV |Double |No cheats, fast and respawning monsters|
+--------------------+----------------------------+---------+---------------------------------------+
Strategies and Hints
Doom is usually a game of fast-paced action. Herein is some advice for navigating it:
Monsters never follow you off of ledges unless they can fly. This includes all but the smallest-gapped stairs (compare the sergeants near the green armor in Doom’s E1M1 versus the zombiemen in the next room).
There is no fall damage in vanilla Doom.
When fighting, never stop moving unless there’s a good reason. A moving target is much harder to hit.
Run. Always run. Walking is only useful for traversing narrow ledges. Most source ports have an auto-run option.
Master the circle-strafe. The player is very fast – take full advantage of this.
Reversing your direction costs you momentum – it’s sometimes better to turn it into a circle-strafe.
Enter big fights cautiously. If you’re afforded a moment to observe, do so and plan. Remember that monsters can be made to engage in in-fighting, especially if they’re different species, if you can get one to take a hit instead of you.
Monsters that are the same species and use a visible projectile attack are immune to infighting and cannot be damaged by those errant projectiles.
Remember that monsters can be made to flinch. The biggest enemies tend to have little pain chance, but many others can be reliably “hitstunned” by rapid or overwhelming firepower, such as from the chaingun or super shotgun. This is invaluable in particular for getting rid of Revenants and Cacodemons. Demons are also easily dispatched this way, especially with a chainsaw.
Sometimes getting backed into a corner is a good strategy if it’s a narrow enough corner to only allow one monster at a time.
Take advantage of pillars and other decorations – no terrain aside from barrels is destructable, so it can be useful for blocking homing missiles or taking cover from fireballs. Mind the splash damage effect when fighting Cyberdemons, however.
Don’t forget that you have an Automap – use it if you get lost. This makes mazes a lot less painful. Be mindful that you can mark important or interesting-looking locations too.
Beware of quiet areas with something important like a key or Megasphere – it’s often a subtle hint that combat is soon to follow.
Similarly, if a map gives you heavy ordinance, especially outside of a secret area, be prepared to use it in the very near future.
Listen carefully to your surroundings – enemies have unique sounds when patrolling, when spotting the player, and when attacking.
Remember that swapping weapons has a time penalty.
Line up your shots carefully – it is often possible to take out multiple enemies with one attack.
Similarly, distance matters, especially when using the shotguns. Make that spread count one way or another. Exercise due caution with rockets for the same reason.
Doom has an auto-aim system that handles the height differentials automatically, but it will always aim for the closest enemy, and it won’t be able to compensate for height differences if the enemy is too far away.
Don’t get too attached to any particular weapon – switch things up based on ammo count and threat level. Don’t be afraid to use your big guns when you need them – nothing is too precious to use if it keeps you in the game.
That said, use the right tool for the job. Don’t use rockets in tight spaces, or when fighting Lost Souls, who tend to charge at inopportune times, for instance. Similarly, don’t waste your more powerful weapons on low-threat enemies; rocket and cell ammo is relatively rare for the most part.
Also, despite appearances, the Super Shotgun does not make the regular Shotgun obsolete – while the former is more powerful per shot, the latter has a tighter spread that’s more useful for sniping, fires twice as quickly, and is more ammo-efficient.
When fighting multiple opponents, especially in close quarters, it’s often helpful to alternate between them with the chaingun or plasma rifle, taking advantage of their flinching in pain if they have a sufficiently high pain chance – this works wonders with chaingunners, for instance.
In general, don’t underestimate the value of rapid covering fire – it can be used almost as a shield as you run by.
A door you can toggle, especially if it’s locked on both sides and only you have the key, can also make for a great shield.
In contrast to the player, all enemies must stop moving in order to aim.
When prioritizing threats, hitscanners such as former humans should often be considered the most dangerous, since there’s minimal potential to dodge their attacks.
Sometimes, discretion is the better part of valor. Don’t be afraid to retreat, if possible, to earlier areas if you’re getting overwhelmed.
Watch your back – it’s not too uncommon to hit triggers that suddenly open a room full of enemies behind you, or send a bunch trickling in via teleportation.
When using teleporters, or lifts where you can’t see the destination, consider switching to a rapid-fire weapon to disorient any ambushers.
Don’t waste pick-ups. As you learn how much health or ammo a given pick-up grants you, learn how to maximise your gains. For instance, if you’re at 99% health, don’t grab a stimpack or medikit – you’ll waste 9 or 24 points of healing respectively. All “extra” health or ammunition gained this way is wasted. Ammo and health management is as much about what you don’t use as what you do.
Prioritise normal health pick-ups over the soulsphere. The soul sphere adds 100 to whatever health you have when you collect it, but stimpacks, medikits, and berserk packs can only affect your health up to 100%. The higher your base health is before collecting the soulsphere, the better.
Similarly, remember that blue armor is more absorbent than green armor. Just because your blue armor is below 100% doesn’t mean it’s necessarily a good idea to pick up a new set of green.
Enemy-specific hints
Every enemy has particular patterns, attributes, and behaviours that can be exploited.
Former Humans
Being fast on your feet and mindful of cover is essential when fighting former humans, especially in mobs. The zombiemen might only be an annoyance, but a shotgun or chaingun to the face can quickly ruin your day, and shotgun guys in particular have an annoying habit of firing just as you’re reloading your own.
Chaingunners are very easy to interrupt.
Hellspawn
Imps have a claw attack, but will almost always prefer to throw a fireball – don’t be caught off-guard, even at close range.
Demons can be baited into attacking and then easily dodged, since they can’t move at the same time and have an extremely low range. They can also be temporarily removed from a fight by being hit by a monster’s projectile if that monster is out of range – it’ll continuously run around in frustration until attacked again or its aggressor is killed.
Cacodemons have a tendency to sneak up on you – always watch your back. When fighting a crowd of them, remember that they have a relatively high pain chance.
Hell Knights and Barons can be thought of as essentially upgraded imps and behave similarly, but have a very small pain chance.
Revenants can be baited into a nearly endless punch-loop at point-blank range, but be careful of retaliatory rockets – rapid-fire weapons are ideal to induce hitstun. When facing missiles, triangular front-to-back movements are very effective.
Lost Souls are committed once they launch, no matter how far they travel; they’ll only stop once they hit a target or a wall. Also, if shot while charging¸ they will likewise retreat until they hit a wall or object. In vanilla Doom, they may also be stopped if they fly over an item. Curiously, Lost Souls are the only monster that forgets its target after every attack, making it unwilling to chase you if you get far enough away. Its 100% pain chance means that the rapid, precise shots of a pistol can be a very effective disabler. Additionally, it is well worth noting that Lost Souls tend to travel in packs.
Pain Elementals are perfectly harmless if you stay at point-blank range, since this will cause their Lost Soul spawns to fail. This does not apply to the Lost Souls spawned upon their death, however. It is also worth noting that they will only attack if the player (or the last monster that struck them) is in direct line-of-sight. It is recommended to destroy the Pain Elemental before going after any Lost Souls it spawns.
Mancubus shots always fire in 3 volleys and follow a pattern: the first two volleys have one shot aimed directly at the player, with the other then being to the right of the player and then to the left; the final shot will instead have one flame to the left and one to the right. As such, be careful of over-dodging.
Archvile fire can be avoided by hiding behind any wall of any thickness, so long as it’s full-height, and the damage can be dramatically reduced by hugging any wall that’s at least waist-high and on the opposite side of the Archvile.
Bosses
To defeat the Cyberdemon, shoot at it until it dies.
The Spider Mastermind must pause a moment to line up shots before firing, which allows barely enough time to duck behind cover.
Finding Secrets
Doom is known for having a lot of secrets, some being quite elaborate, especially in player-made maps. Generally, there are several things to look out for:
If you can see it, you can almost certainly get to it. This was one of the cardinal design rules and is very rarely broken except in the case of obvious decorations, even in player-made maps.
Secret doors are often given away by being a slightly different texture or by being subtly misaligned with the surrounding textures.
Another key indicator is the use of odd textures – over time you’ll start to recognise likely culprits.
Some secrets are activated by shooting, instead of using, the door.
Sometimes there’s also a switch that can be shot, a popular occurrence for some of the more devious player-made secrets. Since you cannot aim up or down in vanilla Doom, note that the Super Shotgun in Doom 2 has a slight vertical spread that is required for some secrets (though this is incredibly rare).
Although vanilla Doom has no dedicated jump key, it is possible to “jump” across gaps through sheer velocity. Much like Super Mario, you can easily cross gaps that are one space wide. Longer gaps are also possible, though tricky.
While the actual need for this is rare, rocket jumping (or taking advantage of an angry Archvile) can be helpful for getting to hard-to-reach areas.
The entrance to areas you can see but can’t seem to get to are usually close by, but sometimes an obscure teleporter is needed.
Secrets usually (but not always) show up on the Automap. If you can find a Computer Area Map you should be able to deduce the location of many secrets based on what rooms you haven’t entered or fully explored. Even without the power-up, the general layout of a map can be telling, such as a feeling of asymmetry.
Illusory walls are insanely rare, but do exist. You can see an example of this in E1M1, in the waste-filled hallway.
Again, listen carefully. Sometimes you’ll stumble across an invisible trigger which activates a hidden door or lift, creating a distinct sound.
If something seems suspicious, try activating or shooting it. Some clever secrets rely more on instinct and subtle, nearly undetectable patterns to be noticed.
Some secrets chain into each other and are impossible to access until their prerequisite secrets are found.
Sometimes a secret’s trigger is activated normally while traversing the level, so it can pay to backtrack now and again.
Because of how the Doom engine works, Z-coordinates (height) aren’t respected when it comes to pressing a switch. To see an easy example of this, look at Doom 2 MAP01. In the room at the left of the hallway, there are two switches, one of which lowers the platforms the zombiemen were on into the floor, and one opening a secret door. Although it seems the former will make the latter inaccessible, if you stand in front of where the switch was you can still activate it despite it now being in the floor. Although rare, some secrets exploit this, and it can also be handy for finding unintentional shortcuts.