The Guardians

From Halopedia, the Halo wiki

Summary

In both Halo 1 and Halo 2, when a player in multiplayer is killed inexplicably (i.e. by a physics glitch, by the environment, or by an AI in Halo: Custom Edition), the message reads "_player_ was killed by The Guardians". There are also ways to do this among players (guardian glitch). For example, aim at a teammate's head with a Battle Rifle (or a Pistol or Carbine), right trigger and Y simultaneously until he dies. Another way is when a player is killed by a melee attack from another player who died just as they did the melee attack. Also being killed in & out of maps by unmanned vehicles has been known to cause this and has resulted in an unexplainable maniacal laugh being heard on occasion. Another more simpler way to see the message is in the level Terminal. If you stand in front of the Train and let it crash into you the sign will pop up at the corner of the screen. You can do this with a Warthog as well, but no one must be in the Warthog, ways to do this, is to drive a Warthog at top speed and get out before hitting someone.

Notes

  • If you do this right, it should show the weapon firing, come down, then immediately fire again without seeing the secondary weapon.
  • Friendly fire must be off to do a guardian glitch on your teammate. Shields off will produce optimal results, but it is possible to guardian glitch with full shields by doing the glitch repeatedly.
  • Doing this while moving will result in you dying instead of your teammate.