Altered Beast is a side scrolling action game that puts the player in control of a centurion who had died in battle. The centurion has been raised from the dead to rescue Zeus' daughter Athena from a Demon God called "Neff" in the Underworld. The player battles undead and demonic hordes, controlling the shapeshifting hero. He must fight through several levels in order to save the kidnapped Goddess. Along the way, the player obtains "Spirit Balls" (power-up orbs which increase his strength and size) from defeating white two-headed wolves. These enable the player to turn into a superhuman (stage one: "giant man", stage two: "superman"...). When three are collected, the hero transforms into a beast with exceptional abilities.