Painkiller Overdose, developed by Mindware Studios, is a standalone expansion of the 2004 game Painkiller. Unlike the original, the player takes on the role of Belial, a half-angel, half-demon seeking revenge for his rejection and imprisonment by both heaven and hell.

The gameplay is similar to the original game, with sixteen levels that take place in various areas of purgatory. The levels consist of arena-like rooms where the player must defeat waves of enemies to progress, and some levels end with battles against huge bosses that require the player to shoot specific parts of their bodies. Completing specific tasks rewards the player with tarot-cards that give Belial special powers. Belial's weaponry is different from Daniel's in the original game, with most weapons having at least two firing modes. For example, the Bonegun can act like a typical shotgun or turn enemies into stone. The game mechanics are familiar, yet entertaining, and the game takes place in various settings like ancient Rome, ancient Egypt, and medieval Japan.