Hall of Mirrors

The Mirror, Mirror on the Wall glitch is a Halo 3 glitch. It can be seen on the second part of The Covenant, and on Sandtrap, The Storm, Isolation and Halo.

On single-player or non-split-screen play, parts of the screen that are affected by the glitch will show a "hall of mirrors" or "afterimage" effect. On split-screen play, affected areas of the screen will show the contents of the other player's screen. The effect is identical to that seen when using Pan Cam outside of a level's boundaries, and it has an identical cause: in 3D, when part of a screen is "empty" -- when nothing, not even a skybox, is rendered on part of a screen -- the contents of the previous frame show through on that screen, creating a "hall of mirrors" or "afterimage" effect. Furthermore, in Halo 3, random red and blue patterns tend to appear in such spaces. When taking a screenshot, a solid color (usually sky blue) fills such spaces.

Affected areas, then, are not surfaces or mirrors -- they're gaps.

Sandtrap
The glitch can only be done in Sandtrap when in Forge. Go into Edit Mode, and fly into the chasm-like structure and face the high dunes that cover up the barrier. Look right, and move forward into the indention of top of the wall just below the ledge and zoom in. You should see the hall of mirrors effect here.

The Covenant
At the beginning of the level, after taking out the (normal) Wraith, if you climb up the surface of the tower you are supposed to enter, you will find a rift in the snow that shows the hall of mirrors effect.

Another hall of mirrors effect occurs in this level. Start the level at Rally Point Alpha. Get into a Hornet and fly to the second tower. Look directly at it and hover down to the left. You will be facing a ledge; fly towards it. Park the Hornet onto the longest ledge, and face the rock wall. Turn left and move forward to a crack in the rock. When you look into it, you will see the hall of mirrors effect.

The Storm
Start the level at Rally Point Alpha on co-op.

During the part with the Scarab Tanks, get two players on a Mongoose, and have them drive against a door and the passenger to alight. If done correctly, the game will freeze for 10 seconds. The Scarab will disappear, and if you go to the door, you will see the hall of mirrors effect.

Isolation
On a variant of the multiplayer map Isolation, called "A Base", the glitch can be seen on the outer wall. If you venture outside the base and past the Mongoose, look at your feet while sticking to the wall. So far along, your feet will start to float, like you are falling. Start to crouch and you will start to fall. Carry on crouching until you hit the grass. If you turn around so you are parallel to the wall, you will see the hall of mirrors effect.

Halo
Start the level at Rally Point Alpha on co-op, so that you begin right after the part where you kill 343 Guilty Spark. One player should move forwards and kill the Flood forces ahead; the other one should remain where they spawned. The stationary player should turn and look behind them. They will see two doors; they need to go to the bottom of the one on the left, and look straight up. There will be a small crack that displays the hall of mirrors effect.