Foundation multi-player map
Successfully complete the game in single player mode under any difficulty setting.
Note: There is a glitch that prevents some people from unlocking the map as it was originally intended. The way it has been done successfully is as follows. Complete single-player mode under any difficulty setting. Create a new profile. Begin a co-op game on the last level with the newly-created profile as the second player. When you reach a section where you fly a Banshee, the new profile must perform a barrel roll and a loop-the-loop. Finish the campaign and the new profile can access the Foundation map when hosting split-screen, System Link, or Xbox Live games.
Alternately, if you have Xbox Live, go to the Microsoft Content download menu. Then, download all recently updated content. Go to a game menu. Go to change the options then change the map. It should be at the very bottom.
Play the game all the way through under any difficulty setting. Throughout the game, there are hints such as "Turn on flashlight", "Go camo with the White button", "Barrel roll with the A button in the Banshee", etc. Do not perform one of these actions (preferably the flashlight or barrel roll) until the very last level of the game. Use it there, and after you finish the game, the Foundation level should be included on your list of multi-player maps.
Hints
Hidden DVD message
Insert the Halo 2 Bonus DVD from the Collectors Edition. Remain idle at the main menu. The Marine will begin to threaten you very comically for not hitting play. He will go through three different routines before it repeats.
Unlimited ammunition
Obtain either a battle rifle or a shotgun. Shoot yourself in the foot until you die. Then, dual wield SMGs, and repeat. If done correctly about four or five times, you should no longer have to reload, and have unlimited ammunition.
Hidden DVD art gallery
Insert the Halo 2 Bonus DVD from the Collectors Edition. Hold [Left] at the main menu until the art gallery appears.
Easy ways to kill hunters
1. For this to work you have to be in two player. One person has to get a sniper rifle or a covenent. Have the other person get a weapon that has a good melee attack. Have the guy who has the sniper rifle or a covenent set up in a location were other aliens will have a hard time getting them. Have the person who has the gun go after the hunter (so he doesnt shoot the other person). While the your parter is in a melee attack with the hunter shoot it in the head or waist. You will kill it after three or four shots.
2. All you Halo freaks out there will remember in Halo:PC & CE you could simply do a little stroll to the left then shoot the hunter it is orange spot to kill it. Well that tactic hasn't completely vanished. If you get your timing PERFECT then you can simply stroll to the side and fill the orange zone with lead (preferably, lead is better than plasma) sustain fire for a short while. After doing this 1-3 times the hunter will be dead. This is especially effective with a sniper rifle. DW Smgs or Magnums.
3. Simply find a fixed turret, the human ones are best and give them a body full of it they will die INCREDIBLY fast. A good place to do this is near the beginning of "Outskirts".
4. When they are approaching (but not charging at you) you can simply fire a shot into their orange stomach and you will kill them with a shot each in easy.
5. Have two people one with a sniper or battle rifle or anything effective and the other with the same. Then get one player to bait the hunter. Then they can fill the hunters spot with bullets however they person behind can hit the more vunerable back area with bullets. And the effectiveness of this is that even if one person dies you will probably win and if the hunters decides to stop bashing you and attacks the other guy then you can fill he's back with bullets and he the front.