Quake

In Quake, there are four difficulty levels: Easy ("This is meant for little kids and grandmas."), Medium ("Most people should start Quake at Medium skill."), Hard ("Here at id, we play Hard skill, and we think you should too, once you're ready.") and Nightmare ("This is so bad that the entry is hidden, so people won't wander in by accident. If you find it, don't say we didn't warn you."

The first three difficulty levels are selected by entering one of three portals at the beginning of the game. Hard mode requires the player to leap over a pit of Lava. Lava balls shoot upward, and if they collide with the player, it will actually stall their movement, causing them to fall into the lava.

The portal for Nightmare difficulty is hidden. Enter any of the three portals and Episode 4. Jump into the Water and hold backwards. If done correctly, you will land on a wooden beam which leads to the portal to Nightmare difficulty. A panel before the portal can be shot to unlock an easter egg in a later level.

The main effect of difficulty is to add more monsters.

Nightmare difficulty makes the monsters' attacks a lot faster. This is mostly seen in the Ogres, who now fire their grenades a lot faster and the Shamblers, whose charge up time to launch ranged attacks is much quicker.

There are two ways to change the difficulty in Quake:

• One is by opening the Console and typing skill, followed by any number from 0 (Easy) to 3 (Nightmare).
• The other is a Teleporter in the episode selection hub that returns you to the difficulty hub, allowing for changing the difficulty level between episodes.

If you use the latter method to change the difficulty after completing The Elder World, you cannot play any other episodes or Shub-Niggurath's Pit on Nightmare without cheating again, depending on the order you play the episodes in. If you don't change the difficulty through either method at any time, then it will remain the same throughout your playthrough. This makes it possible to complete Shub-Niggurath's Pit on Nightmare without cheating, as long as you were on this difficulty before starting The Elder World.

Quake II

In Quake II, there are four difficulty levels: Easy, Medium, Hard, and Hard+. Difficulty level is selected when starting a new single player game. It can also be set via the console using the skill command.

In the original Quake II, Hard+ is a hidden difficulty setting. It can be selected by entering the command skill 3 in the console, followed by map base1 to restart at the beginning of first level. In the 2023 remaster, Hard+ has been renamed to Nightmare and is no longer hidden.

The effects of difficulty setting are as follows:

• More enemies appear on harder difficulties.
• On Easy, the player takes 50% less damage.
• On harder difficulty modes, the player can hold fewer of each item (e.g. Silencer or Quad Damage). On Easy you can hold an unlimited number, on Normal you can hold 2, and on Hard or Hard+ you can only hold 1 of each.
• Enemy AI differs, and their attack patterns are overall more aggressive on harder difficulties. Notable specific differences:
  • On Easy, enemies are 50% less likely to attack, and are also less likely to attack in melee ranged. The Brain won't use its tentacle attack.
  • On Hard, enemies are 200% as likely to attack. Gunners are 50% likely to drop a grenade when they duck. Tanks and Super Tanks won't flinch if hit while firing rockets. Soldiers are more likely to duck and have a more aggressive attack pattern. Mutants are more aggressive.
  • On Hard+, in addition to the effects of hard, enemies never flinch (i.e. enter pain state). The exception is the Gladiator (Beta Class) in The Reckoning, which may be a bug.
• Turrets are slightly faster, react more quickly, and deal more damage.
• Contrary to rumor, skill does not affect enemy hit points, weapon damage, or enemy weapon damage in the base game.
• However, some bosses in the expansions do have more health, as well as other buffs (see especially Nightmare). In Ground Zero, bosses have more health on the harder difficulty levels, and the Black Widow Guardian's ability to use power-ups becomes stronger. In The Reckoning, the Beta Class Gladiator fires three shots per volley with its Phalanx on Hard+ rather than two.

Quake III Arena

In Quake 3, there are five difficulty levels instead of the normal four. All of them can be selected when starting any Singleplayer map. The difficulty levels are "I Can Win", "Bring It On", "Hurt Me Plenty", "Hardcore" and "Nightmare!".

The difficulty setting affects the skill of the bots in each map. The easier difficulties will make the bots inaccurate, handicapped, ignoring the power-ups, very slow to react and turn; whilst the harder difficulties will make the bots fast as a pro player, no handicap, gathering power-ups whenever available, and more accurate than humanly possible, presenting a true challenge.

On "I Can Win", "Bring It On" and "Hurt Me Plenty" difficulties, bots are handicapped; respectively 50%, 70% and 90%. They can only deal a certain percentage of damage and carry limited amount of health and armor, anything above that limit will decay slowly. At "Hardcore" and "Nightmare!" difficulty levels, bots have no handicap and significantly faster react time and turning speed. This forces the player to react faster, aim more accurately and time item spawns to stay alive.

Quake 4

In Quake 4, there are four difficulties, each one represented by a military rank: "Private", "Corporal", "Lieutenant" and "General". The higher a difficulty is, the harder the enemies will be to kill, you will take higher damage from attacks, and enemies' health will be higher. It is not necessary to unlock or discover the hardest difficulty; you may select from the starting menu.