Painkiller Overdose is a first-person shooter, the first stand-alone expansion for 2004 People Can Fly game Painkiller.
Unlike the original game, the main protagonist in Overdose is not Daniel Garner, but half-angel, half-demon Belial who seeks revenge for his imprisonment and rejection by both hell and heaven.
The gameplay is very similar to that of the original game. The game is divided into sixteen levels.
The player must get through each of them slaying hordes of enemies. Most of the levels consist of the arena-like room where you have to defeat waves of monsters to progress. Some levels end up with battles against huge Bosses that require player shoot specific parts of their bodies. The game takes place in different areas of purgatory. Some of them resemble specific historical settings like ancient Rome, ancient Egypt or medieval Japan. Completing specific tasks awards player with tarot-cards that give Belial special powers.
The Belial’s weaponry is different from that of Daniel through most of the weapons are similar in mechanics to their counterparts from the original game. Every weapon has at least two firing modes. For example, Bonegun can act like a typical shotgun or turn enemies into stone; razor cube can rotate metal projectiles at high speed, draw enemies to Belial or slowly shoot metal projectiles.