From Halopedia, the Halo wiki

This article is about the Halo 2 Vista and MCC achievement. For other uses, see Demon.

Demon is an achievement in Halo 2 for Windows Vista and Halo: The Master Chief Collection. It is unlocked by completing any Halo 2 campaign level without dying on Normal difficulty or above.

In the PC version of the game, the achievement is worth 25 Gamerscore and is represented by a flame, with the head of the Master Chief on top. In The Master Chief Collection it is only worth 10 Gamerscore and is represented by a screenshot of the Master Chief aboard Cairo Station.