Nightmare is a modpack created by Yoru, a Steam user that gained a lot of attention for this modpack. Why?!? Because it has fundamentally changed the way Left 4 Dead is played. Every golden rule of the game is broken, in exchange for a more terrifying experience. The pack consists of over 180 addons that all work to impede you for the sake of horror.

The collection also contains a series of ambience mods that add soundtracks from Cry Of Fear and other games to enhance the experience. One of these include an addon called "HellChant" that provides hauntingly beautiful orchestra of infected chior singers that can be heard in the distance while playing. One of the most crucial addons, the Cry Of Fear Color Correction addon, turns the game dark; To the point that your flashlight seems worthless at certain points.