"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". each enemy requires two bullets to destroy.