Doom 3: Resurrection of Evil is an expansion for id Software's Doom 3 which was originally released for the PC in August of 2004. Resurrection of Evil arrived on the PC in April of 2005 and for Microsoft's Xbox in October of the same year. The expansion introduced a few new weapons and enemy types not present in the original Doom 3 but largely kept the gameplay of the original intact, however with a slightly larger emphasis on action. The new weapons consist of a double barreled shotgun and the Ionized Plasma Levitator (effectively a "grabber", similar to the gravity gun in Half Life 2).
The only brand new gameplay addition in Doom 3: Resurrection of Evil is the use of an artifact called the Hellstone, which looks like a human heart. It gives the player a brief period of time to use a key set of powers. These powers include slow-motion, enhanced damage and invulnerability, and are gained by defeating bosses throughout the game. The Hellstone is charged using the souls of dead bodies which litter the levels.