Monitor glitch

"Monitor glitch" refers to two glitches spread across Halo 3, Halo: Reach, and Halo 4. The first glitch, present in Halo 3 and Halo 4, is a state bug that allows a player to appear as a Monitor, but operate weapons as a Spartan. The second glitch, unique to Halo: Reach, is an unexplained bug that allows players to fire Focus Rifle shots as they enter Edit Mode.

Halo 3
To perform this glitch, start a Forge session (networked over Xbox Live) with at least two players on two different consoles. The game settings should grant players unlimited ammo, with Spartan Lasers as the primary weapon. Figure out who the connection host is, and make sure that they aren't also the party leader; the party leader is the target of the glitch, and the host has to leave the session to trigger the glitch.

Have the party leader enter Edit Mode and fly above the connection host. The host should point their Spartan Laser at the party leader. The party leader should select the host's gamertag on the scoreboard, select "Boot Player," and wait at the confirmation dialog. At this point, perfect timing is required: the connection host should charge their Spartan Laser at the party leader, who should boot the host right as the laser fires.

If the host is kicked too early, the party leader will survive. If the host is kicked too late, the party leader will be killed. If the glitch is performed successfully, however, then the party leader should hear two sounds: a Monitor's explosion, and the sound of a Spartan's shields dropping. At this point, the party leader will exhibit traits of both a Spartan and a Monitor: they will have a Monitor's shield HUD, but no crosshairs, and the score will be displayed instead of the Forge budget; and they will have the movement controls of a Monitor, while still being able to fire weapons. The glitched player can enter Edit Mode to spawn items, and will return to their glitched state upon exiting Edit Mode.

Players glitched in this manner are invisible to the connection host; their held weapons, if any, will appear to float through the air. The glitch ends once the affected player is killed.

Halo: Reach
A separate, related glitch is available in Halo: Reach.

To perform this glitch in Reach, start a Forge session with at least two people over Xbox Live. Enter Edit Mode. During the split second when you switch modes, you may notice a weapon crosshair overlaid on the Forge crosshair, and a Focus Rifle icon shown in the top-right corner, as if you were carrying one. If you hold the right trigger as this happens, you should see and hear a brief Focus Rifle shot. This shot can damage players if aimed at them, and if it kills a player, the message "Killed by the Guardians" will appear.

Halo 4
To perform the Monitor state glitch in Halo 4, you must start a Forge session between two players connected over Xbox Live. Note that the connection host cannot perform this glitch.

The player who isn't host should switch from Edit Mode to Player Mode and fall from a great height. Just as they hit the ground, they must return to Edit Mode. If their timing is correct, then they will enter a glitched state similar to that in Halo 3: when they return to Player Mode, they will lose their reticule and editing options, gain the ability to pick up and fire weapons, and see Spartan arms in first-person view; however, they will retain the HUD, outward appearance, and movement characteristics of a Monitor.

Trivia

 * In Halo 3, this glitch can allow players to mimic 343 Guilty Spark's use of weapons in Campaign. A Sentinel Beam can be used to mimic his shots throughout most of his appearances, while a Spartan Laser can be used to mimic his attacks during Halo (level).
 * When the player attempts to perform this glitch on the Gravity Hammer, switching weapons and switching back will make other players see a mini-hammer going through the monitor. [which game?]
 * Sometimes, if you fire your weapon, players may see projectiles coming from random places on the map. [which game?]
 * You cannot use this glitch on mounted turrets, but if they are dismounted, you can pick them up and shoot them. [which games?]

Source
