The Mongoose was originally intended to be put into Halo 2, but was cut and later reworked for Halo 3. The Mongoose prototype did not fulfil Bungie's quality expectations for Halo 2.
"Blow Me Away" performed by the band Breaking Benjamin can be heard as the player approaches the Mausoleum of The Arbiter, as well as during the battle. Though it may sound instrumental, the vocals have simply just been made quieter.
There was a large, unused Flood enemy in Halo 2 called the Juggernaut. Due to conflicting design goals, it wasn't working well in the game, and so was cut. However, it was used as the basis for the Pure Form enemies in Halo 3.
Halo 2 received approximately 1.5 million pre orders before it's release, making it a platinum seller before it even hit the shelves. It made $125 million within 24 hours of it's release.
The PC version of Halo 2 was delayed from release due to an image of a man, who was one of the developers, mooning the camera and exposing his bare buttocks in the game's data (in an error report known as .ass).
There are 21,090 lines of dialogue in Halo 2. Most of these are randomly triggered during combat.
On the level Metropolis, there is a hidden gun known as the Scarab Gun. It is extremely difficult to obtain. It is shaped like a standard Plasma Rifle, contains unlimited ammo and has the same firepower as a Scarab's main turret. In the PC version, there is an achievement for finding it.
Halo 2 is the best selling original Xbox title released, with 8.49 million copies sold. That is over 2 Million more than the second best selling game on the system, Halo: Combat Evolved.
A Soccer Ball is found in the Halo 2 Campaign level Metropolis, hidden in the rooftops. There is speculation that it was used by Bungie to test the physics engine of the game, and that they left it in the level instead of deleting it. It also appears as a Forge item available to place on certain maps in Halo 3, Halo: Reach, and Halo 4.