Hidden Nightmare (Quakes 1 and 2)Edit
QuakeEditIn Quake, it is known as Nightmare and unlike Easy, Normal and Hard, it isn't found in the first part of Introduction. To find the Nightmare portal, the player must enter any of the portals (doesn't matter which one) and then go to the Episode 4 corridor. Enter the Water and step backwards to put the character's back against the wall behind. After falling through the Water, the player should be on a wooden beam looking down on the gate that leads to the Slipgate. Follow the beam to the corridor in the left hand side and around the corner there is a Lava Teleporter with the word Nightmare written down on both sides.
Nightmare makes the monsters even more deadly, giving them faster reaction times and attacks. For example, the Shambler can now fire its lightning beam twice as fast and Ogres can now launch the grenades at an alarming rate.
Quake: Scourge of ArmagonEdit
At the beginning, go through the hallway marked "Normal". Continue on until you reach the room with the Normal difficulty slipgate in it. Instead of going through, take the hallway to the left. Eventually you'll find a large pile of crates. Climb onto it and you'll find a hidden elevator. Take it and you'll find the slipgate that leads to Nightmare.
Quake: Dissolution of EternityEdit
To access DoE's Nightmare, you need to activate three buttons. Enter any of the difficulty portals. Walk forward until you're at the entrance of the two episode selection rooms. Go around the wall on either side to see a small area with a lamp hanging from the ceiling. There is a button next to the lamp on both of these sides. Shoot them both. Now find the portal that takes you back to difficulty selection. Shoot into it and you'll trigger the third button. Go back to where you teleported in (marked by a square tile) and look up. You should see a tunnel in the ceiling filled with lava. Stand under the tunnel in a certain spot and an elevator will raise you into it. You will be teleported into a room containing the portal that takes you to Nightmare.
In Quake II, Nightmare is renamed to Hard+. To play Hard+, go to the console and type in "Skill 3" (Easy=Skill 0, Medium=Skill 1, Hard=Skill 2, Hard+=Skill 3) and then type "Map base1". This will start the game from the first level on the difficulty level. Hold F1 to see the objectives and in the top right hand corner, it will say which difficulty is in effect. Trying to start the game like normal from the menu will result in it going back to the difficulty level you chose in the menu. Typing in "Skill 3" will not change the setting until the player starts a new map.
Differences introduced in Hard+ include faster enemy attacks and enemies with more health (one example of this is the Carrier, who has 3,000hp in Hard but 4,000hp in Hard+). But the main difference is that monsters will never go into pain (unlike in Quake 1 where enemies went into pain the first time you hit them). All if not most enemy data on this wiki is taken from the Hard difficulty.
Quake 3 and 4Edit
In Quake 3 and 4, the Nightmare difficulty can easily be accesed from the list of difficulty levels before playing a game. In Quake 3 it is known as Nightmare, but in Quake 4 it is called General, as the difficulty levels are named after military ranks as opposed to Easy, Normal, Hard.