Mortuum is an arcade game in which you play Cruentus, an undead witch-king. You must fight your way through many levels using your sword and magic. Your sword is controlled using directional keys, and swinging your sword at an enemy will damage it more than stabbing it. Each level is completed when you cast a gate spell and go through the gate, but if you spend too much time in a level, the Angels of Mortuum will come after you.