Phantom Slayer is, hands-down, one of my favorite games on the Coco. Released in the first half of 1982, it was one of the first full screen, real-time 3D first person shooters done for any platform. It featured multiple skill levels, randomized mazes every time you played (both easy and hard ones), and monsters (phantoms) that took an increasing # of hits before they were killed. It also featured a teleport charge square, which, if you found it, would charge you up to teleport back to the middle of the maze instantly (and show you the overhead map briefly) if you got in trouble. Of course, if there happened to be any actual phantoms near there, you were probably dead...
Title: Phantom Slayer
Author: Ken Kalish
Publisher: Med Systems (later Screenplay)
Released: August 1982
Requires: Color Computer 1,2,3, 16K RAM, tape or disk.