Denizen is a science-fiction action flip-screen maze game, with a top-down perspective. The player controls a marine, with the aim of detonating twenty explosive bolts on each of three levels. The marine is armed with a rifle and is initially supplied with 99 bullets. The player can only move orthogonally, in half-tile steps. Each screen may contain one or more enemies, who move toward the marine in a straight line until they reach an obstacle. The enemies attack the player merely by contact, draining the character's health in a manner similar to Gauntlet.[2] Each enemy requires two bullets to destroy.
Health is regenerated by returning to the marine's start point on each level. If he is out of ammunition, this also supplies him with a single bullet. Items that can be collected include single-use keycards to open locked doors, ammunition, and a torch which allows better vision in dark areas.
