Backwash

Backwash is a multiplayer map featured in Halo 2. It was added to Halo 2 as part of the Maptacular Pack.

Summary
Backwash is one of the most unplayed levels on Halo 2. It is a mid sized multi-player level in Halo 2, resembling the Halo: Combat Evolved campaign level. It is a large swamp set on Delta Halo. You can tell it is Delta Halo, not Alpha Halo, as 2401 Penitent Tangent can be seen floating around and humming to himself, and the architecture of the buildings differs from that of Alpha Halo. It is actually stated by the developers of Halo 2 that Backwash was originally set on Alpha Halo and based directly on 343 Guilty Spark. It is also stated that they originally had 343 Guilty Spark floating around but decided to change him to 2401 Penitent Tangent because the blue glow of 343 Guilty Spark's eye could too easily be mistaken for a Plasma Grenade flying through the air.

Matchmaking Removal
Backwash was removed from Halo 2 Matchmaking in the April 2006 Matchmaking Playlist Update (NOTE: Not an Auto-Update), due to problems with the Xbox 360 loading the fog covering the map. To this day Backwash remains the only map to ever be removed from Halo 2 Matchmaking.

Hidden Message
There is a way to get out of the level, but it requires super-jumping or a Spectre. With a person, get him/her to Superjump over the invisible wall on the hill, then get them to stand on top of the base (red or blue). Get them as close as possible to the wall and then sword cancel up onto a small spot on top of the base. You can now sword cancel (try it a lot) through the wall. Then, walk through something that looks like a large amount of roots (surrounds the outside) and look for edge of the level. Then walk around until you find red ground. The message is very large, written in blood, and says: Looking a little rough out here. (Possibly because of the mold, fog, etc.) Also, go to the far right and there is a message that simply reads, "HERE."

To do it with the Spectre, go to blue base and jump on a small ledge that is right next to the invisible wall. Have the driver put on a severe handicap (if you don't have an overshield) then ram into you. If done correctly you will be smashed through the invisible wall.

Strategy
Try to limit use of all Covenant weapons on this map, as the fog shows the plasma bursts very easily. This especially means either not using the energy sword at all, or keeping it hidden until right before you attack. And no, using the invisibility power up on the level will not solve this problem, seeing as in Halo 2 energy swords are still visible no matter what you do.

Trivia

 * If you listen closely, telephone ringing can be heard in a distance of the map though, it could be the sounds emitted by the Monitor as it hovers around the map.
 * Though the sounds made by 2401 Penitent Tangent on this level are similar to sounds from 343 Guilty Spark's files, they were recorded by a different voice actor and are therefore distinct.
 * Flood gurgles can be heard around the place. An easy way to hear them is to go into the bases (small buildings on the sides of the map).
 * Backwash was used as The Great Swamps in Red vs. Blue.
 * Elements of Backwash may have been incorporated into the Halo 3 map,, another Flood-themed map.
 * Along with, this is the only level in the Halo Trilogy to spawn a Sentinel Beam by default.
 * There was a game type called Predator that was designed for use on this map. It was a variant of Juggernaut in which the Juggernaut was fast, invisible, had radar, had an Energy Sword and was only supposed to use melee based attacks. The other players were only allowed to use the Battle Rifle and had no radar and therefore required a lot of teamwork to take down the Predator. The fog made it almost impossible to see the Predator (at least from a distance) meaning that the other players had to stick together. Also, neither the predator or the other players had energy shields. This made for a very "spooky" atmosphere. This could be a reference to the movie Predator, as the alien in that movie had very similar traits to the Juggernaut, as well as being named the same.
 * There is an Easter Egg called Hidden Gargoyle on the map.