Insmouse no Yakata is an action game where the player must survive many mazes filled with mutated monsters. When starting a new game or loading a password the player starts with three hearts and six bullets for their revolver, but more health and ammunition can be found randomly in each maze. The goal of each maze is to first find a key and then locate the exit door while avoiding monsters when possible. Finishing a level quickly will put the player on the path of harder mazes as well as the best ending.