Time Travel Glitch

The Time Travel Glitch is a glitch present in Halo 3 's Campaign level The Covenant. The glitch allows players to "travel back in time", going back from the Scarab Tank battle to the third tower; it can also be done in reverse.

General Method
Basically, a player has to go to the Scarab Tank battle and find a way to glitch themselves over the mountainside to the left of or behind the second tower. From there, they need to move into the void. After traveling into the void for a little while, they will find themselves "warped" back to the third tower's exterior.

The glitch can also be done in reverse. If a player manages to glitch themselves onto a mountaintop at any outdoor point before they ascend the icy slope next to the third tower (said slope leading to the Scarab Tank battle), they can travel "forward" in time by simply crossing over into the Scarab Tank area.

Instructions (Going Back)
One method involves driving a Prowler up a certain cliff in the Scarab Tank area, glitching it over the wall and into the void. Once the player has reached the edge of the void, they must slowly back into the void. At some point, the player will be teleported on top of the cliffs in front of the towers. From there, they may enter any of the three towers.

Instructions (Going Forward)
In Co-op, on the way to the first tower, you or your companion should grab a Ghost. Clear out the enemies at the first tower's entrance, and then go up the hill that leads to the Shade. Have one player (Person A) pilot the Ghost, and the other (Person B) stand on top. Person A should ease the Ghost against the cliff wall, and the use the boosters to propel it to the ledge of the tower. Person B should jump when closest to the tower. If done right, Person B will land on top.

Person B should then travel to the next ledge and grenade jump up. Person A should kill themselves so that they spawn near Person B. The two players should then continue to ascend the cliff. When they get to the point were they cannot go any farther, they should jump to the right and land on a invisible wall. The players will be in their jumping pose, but they will still be able to float their way up the snowy cliff. Keep going and the game will freeze temporarily; after the delay, the duo should be teleported to the other side of the barrier: the Scarab Tank area.

Alternatively, a player can hijack the Wraith in the valley, park it on top of the destroyed Shade, get out, and then grenade jump from it onto the cliff. At this point, the player would continue as they would in the previous method after grenade jumping. Upon reaching a mirror-like graphical glitch, the player would go to the corner of the tower where the snow first meets the tower (away from the mirror). From there, they would walk into the little crack between the snow and the tower. At that point, the game will freeze temporarily, and after the delay, the player will find themselves behind the tower, able to explore the area but unable to return to the other side.

Bear in mind that additional kill barriers may be present.

Instructions (Forward and Back)
It is possible to explore the exterior of the level using a Hornet. To do so, have one player (Person A) gather a Plasma Pistol or a Power Drain. Person A should then "go forward in time" using a Ghost, as described above. At least one other player (Person B) should continue the level as normal, right up to the point where the Scarab Tanks land.

At this point, Person A should stay on the mountainside, keeping a watch out. The Hornets that are deployed into the area as reinforcements are flown in from Person A's position. When Person A spots a Hornet, they should immediately stop it by deploying their Power Drain or firing an overcharged Plasma Pistol shot at it. They should then hop into the vehicle, and travel back in time by flying over the cliff and into the void.

From there, Person A may freely explore the seaside portion of the level.

Aftereffects

 * The area will reload, and terrain will reappear.
 * Actors should be missing. In other words, no enemies, vehicles, Scarab Tanks, or other interactive objects should be present. There seem to be exceptions to this rule, including a small number of "hidden" Marines and any partially-infected Brutes (see below).
 * At least one hidden Marine may be present in an area "by default", explaining his presence. The Marine in question appears at Tower 3 when traveling back in time, standing in exactly the same spot as another Marine, who stands waiting by a set of UNSC vehicles after you wipe out the Flood at the tower's entrance.
 * The partially-infected Brutes' status (as being partially infected) may have prevented the game from removing them as you passed through loading points on your way to the Scarab battle.

Uses

 * This glitch can be used to enter the second tower. Tower 2's interior is an exact replica of Tower 1, save for the fact that it is completely empty. There is even a missing space where the Terminal would be.
 * This glitch can be used to access the Secret Room On The Covenant.
 * If, during Co-op gameplay, you activate a loading point and leave the area just as a Brute at Tower 3 is being infected by the Flood, then you can travel back in time and confront the partially-infected Brute later. The Brute will be covered in random sacs of Flood biomass, but it will behave mostly like a normal Brute -- its AI will be glitched. At times, it will stand idly in a battle-ready pose, even allowing players to walk right up to it; at other times, it might suddenly attack.