Hall of Mirrors

The Mirror, Mirror on the Wall glitch is a Halo 3 glitch where surfaces are reflective when they should not be. It can be seen on the second part of The Covenant, and on Sandtrap, The Storm, Isolation and Halo.

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 will either see a reflection of yourself or what your opponent(s) are doing.

The Covenant
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 a reflection of either yourself or of whatever your co-op partner happens to be doing.

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 a mirror reflection.

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 your Co-Op buddy. This must be done on local with a friend or you will see double vision.

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 a part of the other player's screen.