Hall of Mirrors

This glitch can be done on the second part of The Covenant and on Sandtrap.

Sandtrap
For the Sandtrap part, this must be done in Forge mode. Go into Forge mode, go into that chasm type thing 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
For the Covenant, skip to 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, go there. 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 in it, you will see yourself or whatever you're co-op partner is doing.