The Gun Beetle is a robot created by the military organization, G.U.N., and is part of G.U.N.'s Beetle series of robots. It appears as a enemy in Sonic Adventure 2, Shadow the Hedgehog, and Sonic Generations.
It is more advanced than the Mono Beetle, as it has a gun attached to its underside. In Shadow the Hedgehog, the Gun Beetle carries a variety of guns which can be picked up when destroyed. In other appearances, it shoots a single projectile.
In Shadow the Hedgehog, in a number of stages, it's full name is a 'G.U.N beetle drone sentry'.
In Sonic Generations, it appears from the G.U.N Truck in Classic City Escape, where they fire single projectiles again.