The demon rune is an item in the 2016 Doom reboot which occurs only during multiplayer game play. It appears as a floating red pentagram with a set spawn point. It transforms a player into one of several powerful demons when touched.
When taken, the player who obtains the demon rune will be transformed into a demon they selected before the match. The demons currently available for use are, (in order of unlock) the Revenant (which is unlocked by default), the Baron of Hell, the Mancubus, and the Prowler. This transformation lasts for a total of 60 seconds, after which the player will revert to his or her human form if they have survived. Although each demon is powerful in its own right, it is possible for enemy players to kill the player who has become the demon, and doing so will cause the demon rune to drop, where it can be collected by any other player to transform and lay waste to his or her enemies.
The demon rune will otherwise eventually respawn, with its reappearance announced verbally to all players in the game 15 seconds beforehand with the message, "Demon rune spawning in 15 seconds."