Unlockable: Foundation Multilplayer Map
Unlock the hidden Foundation level in Halo 2 multi-player by completing the single player campaign on any difficulty.

Blind Mode: At the beginning of Outskirts jump on top of the light on top of the door with a crouch jump, then jump to the left platform. Turn to your left and go down the long dark corridor and pick up the skull.

Envy Mode: On the level "Delta Halo" on Legendary Difficulty, find the Envy Skull atop a building to use Active Camoflage like the Arbiter.

Grunts Birthday Party Mode: In the level Arbiter on Legendary, fly to the bottom of the map to find grunts dancing around a skull.

Dual Wielding weapons: Human Pistol, Plasma Pistol, SMG, Needler, Plasma Rifle, Covenant

When you dual wield you bring death to your enemies, but you cannot throw grenades, Melee attack, and reloading takes much longer.

Tactics: If you are in a closed area hold only 1 weapon so you can throw grenades. If you are in an open area have 2 weapons in hand because grenades will be useless.

Foundation multi-player map: Successfully complete the game in single player mode under the heroic difficulty setting.

Unlock New End Movie: Beat the game on the Legendary setting to unlock a longer, different final movie.

Alternate ending sequence: Successfully complete the last level of the game in campaign mode under the legendary difficulty setting. The new ending features a human and alien fighting hand to hand.

Defeating Grunts: When the Grunts are sleeping you can beat them to death with the butt of your gun without waking up any of the other Grunts.

Infinite Grenades: Go to the multiplayer screen, go to edit game types to make up your own game type.