Overload glitch (Halo 3)
From Halopedia, the Halo wiki
For the Halo 2 Overload Glitches, see here.
The overload glitch is a bug present in Halo 3. When too many objects are present in a map, the map becomes "overloaded", resulting in the deletion of the "oldest" objects. The glitch can be set up in Forge, and can be performed in Custom Games or Forge. One Campaign level is also prone to the bug.
Overloading a map is usually done to disable certain map features that prevent players from leaving a level's boundaries. Such features include the Brute Landmines on Sandtrap and the watchtowers on Sandbox.
Eventually, the Trip Mines will explode on their own; this is because a Trip Mine will automatically detonate after 90 seconds. After this explosion, the map should be overloaded. Sometimes, however, the trick must be repeated in order to have a noticeable or useful effect. (In such cases, the Trip Mines usually reappear after the first explosion.)
In some cases, the Trip Mines may start to disappear in a blue flash. If this occurs, then the map is overloaded.
Note that you can drop Trip Mines faster by obtaining a second weapon and repeatedly pressing X and Y -- two X presses for each Y. (X + X + Y + ...) Note also that this fast method can increase the game's RAM usage, possibly leading to a crash.
Currently, only The Covenant can be overloaded, by using two exploits. The first causes a large amount of Marines to spawn; the second, which requires Co-op, allows players to accumulate Hornets in the level.
During the first Hornet battle, when the Master Chief flies to Tower 3, both players should fly to the island in front of Tower 2. They should dismount their Hornets, such that the vehicles fall into the sea, but the players land safely on the island. A Marine should quickly fly another Hornet to the island.
At this point, one player (Person A) should fly the Hornet away, while the other (Person B) remains on the island. Person A should land the Hornet at a location that Person B cannot reach. Person A should then die; they will respawn with Person B. A Marine will bring a new Hornet to the island; the two players should repeat the process.
Eventually, the accumulation of Marines and unreachable Hornets will overload the map. If a player uses a Hornet to proceed to the next loading point, the other player will be transported forward, and all the Marines and Hornets will be removed from memory, ending the overloading effect.
Saving an overloaded map
Start a Forge session. In an out-of-the-way area that players can't reach (preferably outside the map), make a big pile of weapons and equipment. Once a large amount of items has been placed, spawn a scenery item on top of the pile. If it disappears, then place a bunch of movable scenery on it. Otherwise, keep trying.
When enough scenery has vanished, start a new round. If enough items have been placed, the map will be overloaded, and will be overloaded the next time it is loaded.
Some more specific instructions:
Overloading tends to disable the "built-in" special features present on several maps. Sandtrap's Elephants will vanish. Lifts, such as the air lift on Blackout, will stop functioning. Epitaph's floating platform will fall. Most notably, the The Guardians' scripted appearances (on Sandtrap, Sandbox, and Snowbound) will stop functioning.
However, overloading a map may cause the game to use a lot of memory (since there are so many objects that need to be processed and kept track of). The game's stability can decrease; lag is a likely result, and the game may even crash.
Specific Effects by Level