How to Get the Scarab Gun in Halo 2

The scarab gun is the most powerful weapon in the Halo games. It has unlimited ammo, never overheats, and has a sustained firing rate, however if this weapon is fired too close to your position it will cause instant death. It's in the form of a Plasma Rifle but fires like the main cannon of a Scarab. It is found as an easter egg in the level Metropolis.