Looking like he just stepped off the set of Videodrome, Bushwacker is an mercenary with guns for arms.
Taking one of the stranger career paths in the Marvel Universe, Carl Burbank was initially a priest before he quit his vows to join the CIA. They outfitted him with a cybernetic arm and turned him into an assassin. He eventually quit to work as a freelancer.
Bushwacker's arms are able to transform into any kind of gun, morphing from a pistol to anything from an assault rifle or a shotgun to a full on grenade launcher. Initially it was just his right arm that could transform, but he was later upgraded so that both arms could do it.
Apart from looking absolutely disgusting, the main issue with Bushwacker's powers is how the hell they're supposed to work. Sure his arm can turn into a gun, but what about ammo? Does he have to stop mid-fight to reload his arm? Really the whole thing seems needlessly elaborate for a man whose superpower boils down to "has a bunch of guns".
Also, despite one of his defining characteristics being a hatred of mutants, Bushwacker is actually mostly an enemy of Daredevil and the Punisher. Although, he did try to fight Wolverine once and got stabbed in the throat so that might explain his reluctance to tangle with the X-Men.