What gun in halo 2 (xbox not computer or "PC" as some call it) was found only once (as far as i know) in the entire game? only in the campaign in one level, not multiplayer. This gun is placed where you would have to be lookin around for somethin, people don't just drop these sort of things you know.
You're talking about the Scarab Rifle found in Metropolis I assume. You had to get a Banshee to follow you through some tunnels, and once you got through a checkpoint, you would board it and fly up to a large bridge-like building, and it would be up there. Looked like a Plasma Rifle, but shot Scarab projectiles. As far as I know it was the only secret weapon.