Shotgun is a common weapon in the mod series, created by Shadow The Worm, which appears in all story builds except for Worms: Utimate Golf.
Shotgun is a two-shot weapon, meaning, that its user can fire 2 shots in one turn. After the first shot is fired, the shotgun takes some time to reload and prepare for the second shot. The shotgun allows the user to move beetween the shots, making it a great weapon for tactical use. Despite the single shot damage being quite low (25 HP per shot), the max damage is higher, than Handgun's all-bullet damage and Sniper Riffle's headshot damage. When the Icarus Potion is used, the shotgun becomes even more useful, due the wings not disappearing until the second shot is fired.
There is a cheat in Ultimate Worms Project, which turns the Shotgun into a Limit Break weapon.