The Catacomb Abyss is one of the first ever first-person shooters. It's based on an early id Software raycasting engine, similar to the one used in Wolfenstein 3D (which came months afterwards) but in 16 colours.
You play the role of a magician, who is once again called upon by the townspeople to defeat his ancient archrival Nemesis again. After having defeated Nemesis in the past, his minions have erected a huge museleum in his honour, and as a result the townspeople are forced to live under a rule of horror. You must once again venture into the catacombs, defeat Nemesis and free the townspeople.