Each game skill level provides general difficulty settings that allow a greater variety of players to enjoy the game, allowing novices to face fewer opponents even with advantages for the player, and giving those who have mastered the game a challenge against many monsters, possibly with enhanced aggressiveness. Each skill level bears a colorful name suiting the character of the particular game being played and can be selected when the game starts or through additional options, particularly the -skill parameter.
Doom engine games
|Skill||Menu name||Source code1||Thing placement2||Ammo3||Special|
|1||I'm too young to die.||sk_baby||The same as in sk_easy||Double||Players take half normal damage|
|2||Hey, not too rough.||sk_easy||Least numbers or strength||Normal|
|3||Hurt me plenty.||sk_medium||Default numbers or strength||Normal||Used unless otherwise defined by the user|
|4||Ultra-Violence.||sk_hard||Greatest numbers or strength||Normal|
|5||Nightmare!||sk_nightmare||The same as in sk_hard||Double||No cheats4, fast5 and respawning monsters|
- This is the name or tag for each skill level according to the source code.
- Each thing placed in a level (except for player starts) has cumulative bit flags (easy, normal, hard) marking on what skill levels it appears. The difference mainly amounts to larger and tougher comportments of monsters on the harder skill levels, but may also account for changes in the location of certain things. For example, in E3M6: Mt. Erebus the blue key is located in different places depending on the skill level.
- Double means twice as much ammo is added to the player's current total when a corresponding item is picked up. For example, a rocket will provide 2 rockets, 4 shotgun shells will be counted as 8 shells, and a box of bullets will provide 100 bullets instead of the usual 50.
- All cheat codes except idclev and iddt are disabled. Some source ports may change this or have internal workarounds.
- Monsters attack more rapidly, demons and spectres move faster and several monster fireball types fly faster.
The 2019 re-release introduced a new skill between Ultra-Violence and Nightmare!, entitled Ultra-Violence+. It behaves as UV with fast monsters but also enables the spawning of multiplayer-only map things in single player mode.
Heretic skill levels
|Skill||Menu name||Source code1||Thing placement2||Ammo3||Special|
|1||thou needeth a wet-nurse||sk_baby||The same as in sk_easy||+50%||Players take half normal damage, keys are shown on the automap|
|2||yellowbellies-r-us||sk_easy||Least numbers or strength||Normal|
|3||bringest them oneth||sk_medium||Default numbers or strength||Normal||Used unless otherwise defined by the user|
|4||thou art a smite-meister||sk_hard||Greatest numbers or strength||Normal|
|5||black plague possesses thee||sk_nightmare||The same as in sk_hard||+50%||No cheats4, fast monsters5|
See the Doom and Doom II table above for specific notes, as there are no differences in general, except that +50% means one and a half times as much ammo is added to the player's current total when a corresponding item is picked up.
Hexen skill levels
|Source code1||Thing placement2||Special|
|1||squire||altar boy/novice||apprentice||sk_baby||The same as in sk_easy||Players take half normal damage. +50% mana. Automatic use of Quartz flasks and Mystic urns.|
|2||knight||acolyte/missionary||enchanter||sk_easy||Least numbers or strength|
|3||warrior||priest/acolyte||sorcerer||sk_medium||Default numbers or strength||Used unless otherwise defined by the user|
|4||berserker||cardinal/initiate||warlock||sk_hard||Greatest numbers or strength|
|5||titan||pope/mystic||archimage||sk_nightmare||The same as in sk_hard||No cheats4, fast monsters5. +50% mana.|
The alternate righthand titles for the Cleric are used on the N64 port.
See the Doom and Doom II table above for specific notes, as there are no differences in general.
Strife skill levels
|Skill||Menu name||Thing placement||Ammo||Special|
|1||Training||The same as in skill 2||Double||Players take half normal damage; monsters move at half-speed1|
|2||Rookie||Least numbers or strength||Normal|
|3||Veteran||Default numbers or strength||Normal||Used unless otherwise defined by the user|
|4||Elite||Greatest numbers or strength||Normal|
|5||Bloodbath||The same as in skill 4||Double||No cheats; fast monsters2; Robots, Templars, and turrets respawn|
- Acolytes and stalkers move, attack, and react to pain half as fast. Reavers and ceiling turrets attack half as fast. Crusaders attack and react to pain half as fast. The Bishop's homing missiles move twice normal speed (see Bishop's missiles have reversed skill properties).
- All monsters attack aggressively. Acolytes move, attack, and react to pain twice as fast. The Bishop's homing missiles move at half-speed.
For other relevant notes, see the Doom and Doom II table above.
Doom 64 skill levels
|Skill||Menu name||Thing placement|
|1||Be Gentle!||Same as "Bring it on!" but adds double ammo and the player receives half damage|
|2||Bring it on!||Lesser numbers or strength of opposition|
|3||I own Doom!||Greater numbers or strength of opposition|
|4||Watch me die!||Greatest numbers or strength of opposition|
Non-Doom engine games
Doom 3 skill levels
|0||Recruit||The Marine takes 75% of the base damage. Slightly fewer monsters than usual are encountered.|
|1||Marine||The Marine takes 90% of the base damage.|
|2||Veteran||The Marine takes 170% of the base damage.|
|3||Nightmare||The Marine takes 350% of the base damage. All medikits are removed from the game, and the player's health steadily drains until it's 25 or below. To restore health, the player must use the Soul Cube (Artifact in RoE), or health stations. Player starts the game with respective artifact in their possession. Number of monsters is the same as on Veteran skill. This skill level must be unlocked by first completing the game on any other skill level.|
The difficulty setting can be controlled by the console variable g_skill. The damage changes take effect immediately, but a map restart or change is necessary for the rest. For example, if a player begins the level on Recruit difficulty and then enters
g_skill 3 in the console, immediately their health will begin its drop to 25 and they will receive Nightmare damage. However, the Soul Cube is not given, medkits remain in the level, and the amount of monsters does not increase.
Nightmare mode must be unlocked by completing the game first. This can be bypassed by changing the console variable g_nightmare.
Doom (2016) skill levels
|0||I'm Too Young To Die||The marine takes around 25% less damage from enemies. Gauntlet sections have fewer enemies.|
|1||Hurt Me Plenty||The standard difficulty. The marine takes normal damage and enemy numbers are unchanged.|
|2||Ultra-Violence||The Doom marine takes roughly 50% more damage and enemy numbers are increased. Additionally, health/armor pickups and ammo dropped from Chainsaw kills yield fewer supplies, making health, armor and ammo scarcer.|
|3||Nightmare||The Doom marine takes about 90% more damage from enemy attacks to the point where a melee attack from an imp at the start is capable of one-hit killing him if he does not have health upgrades. Additionally, health/armor pickups and ammo dropped from Chainsaw kills yield hardly any supplies, demanding that the player conserve their resources at all times.|
|4||Ultra-Nightmare||Functions the same as Nightmare, but with the addition of Permadeath, meaning the player will need to complete the entire game without dying; saving is disabled apart from an automatic save in between stages, and if the player dies outside of a Rune Trial for any reason they must restart the game from the beginning. Skulls are left behind in the location of a player death as a progress marker. Depending on the version, this mode may be locked or unavailable altogether.|
Doom Eternal skill levels
Doom Eternal shares its skill levels with its predecessor, with the addition of Extra Life Mode. Similar to Ultra-Nightmare, Extra Life Mode is a Permadeath mode that can be applied to any skill level save for Ultra-Nightmare. When it is active, running out of extra lives will cause a Game Over in the same manner as dying on Ultra-Nightmare, erasing all progress in the campaign.
- In addition to the five Doom standard skill levels, in vanilla Doom a skill level of 0 can also be specified, but only using the -skill parameter. Doing this empties maps of all things apart from the player starts. This does not work in many source ports. It also renders many levels that have boss trigger effects, require keys or use teleporters impossible to finish without the aid of cheat codes.
- Early versions of Doom did not support "Nightmare!" skill. The initial mail-order releases were version 1.1 and only included the first four skill levels. The widely circulated version 1.2 added "Nightmare!" skill support. "Nightmare!" was added with the characteristic dark humor of the Doom games in response to any comments saying the game was too easy on "Ultra-Violence." After selecting "Nightmare!" from the main menu, the player is asked "Are you sure? This skill level isn't even remotely fair." The player must then confirm that he wants to play on Nightmare mode, a step which is unique to this skill level.
- The name of Doom's fourth skill level, "Ultra-Violence", comes from a phrase in Anthony Burgess's 1962 novel A Clockwork Orange, via Stanley Kubrick's 1971 film version.
- In the Doom alphas, "I'm too Young to Die" was called "I Just Want to Kill", hence the name M_JKILL for the graphic for skill 1.
- Doom's "I'm Too Young To Die" skill level was re-named "I am a wimp" for Atari Jaguar, 3DO, Sony PlayStation and Sega Saturn versions.
- Some skilled players have created new challenges by defining custom rules, such as pacifist (not hurting monsters) and Tyson (fists, pistol, and chainsaw only).