The AP4 Saw is a boss. It is encountered shortly after getting the hook shot. It consists of a tire with some metal plating covering the side and front of the tire. On its side is some sort of red light, which due to its position looks like an "eye". It can go up walls and ceilings, and it occasionally fires missiles out of some unseen launcher, but it is not a problem. It must be shot in the unprotected back, which takes a while, making the boss fight take a bit despite it posing little threat.