O.D.T. is an action role-playing game with some platforming and puzzle-solving elements. The player can choose to control any of the four characters. Each of them has his/her own strengths and weaknesses: for example, Maxx has high defense, while the archbishop has access to powerful occult techniques. Defeating enemies rewards the player with experience points, which can be used to increase a particular parameter of a character, increasing his/her combat abilities.