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 changing 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 one of five demons; a Revenant, Baron of Hell, Mancubus, Prowler, Harvester, Cacodemon, or Spectre. (The Harvester, Cacodemon, and Spectre are DLC-only demons.) The demon that the player transforms into is chosen at the start of a round. 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. It is possible for other players to kill the player who has become the demon, and doing so will cause the demon rune to drop and nets the player who kills the demon a Demon Slayer award.
A dropped demon rune will be locked for a short time for the team that had the demon, and instantly available for the opposite team. In any instance, the player that collects the dropped demon rune will have a shorter play time as the demon. 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." The powerful Gauss Cannon is primarily meant to exist as a counter to the powers of the demon rune.