Half-Naked Guy

In the final level "Halo," there is a secret area for the 7th Marathon Terminal. Aside from the terminal's hallway, there are two rooms: one bright room with a vertical energy beam in the center, and a dark room with a horizontal energy beam and lethal chasm.

It's hard to tell by standing at the edge of the chasm, but there is a small nook on the left side of the room (left, as if one looks out over the chasm). It is not known whether a player can rocket/grenade jump there, but by watching save film, one can detatch the camera and move in there.

In the far corner of the nook is an eerie billboard of a human form facing the wall, apparently with its hands behind its head.