Telefrag

A telefrag is a special kind of frag or kill that results when a player or monster stands on the location of a teleporter as another player teleports to that location. The monster or player who was originally standing at that location will instantly die. Telefrags can be strategically used by a Doom player to kill powerful monsters without using any ammo.

The PWAD mkfrgtme.wad from Maximum Doom uses a special effect in which a player in a single-player game can self-telefrag. (It is at the western side of the map.) The effect is created by placing a second "player 1 start" Thing at the teleport landing site.

The PWAD nopanic2.wad, also from Maximum Doom, also has a second "player 1 start" Thing. It appears as a green player (that is, a marine). If you shoot at the marine, you may push him into the nearby teleporter, and he will teleport. If you then follow him into the teleporter, you will self-telefrag as above.

Utilizing an intentional telefrag is considered cheating in a UV_pacifist speedrun.