From their website:
When a commando squad reaches an entrenched enemy position, its gunners prepare for action. In a coordinated assault, the commandos overrun the position, cutting down sentries while the scattergunners fire into concentrations of the enemy. The blast of grapeshot is unbelievably lethal in the close confines of a trench. A coordinated commando assault supported by grenades and scatterguns rapidly turns units of enemy of soldiers into ground meat.
Trencher Commando Scattergunner comes in a blister (PIP 31066). A player may field up to three Trencher Commado Scattergunners for each Trencher Commando unit (PIP 31064) in his Cygnar army (so up to six total for each warcaster in his Cygnar army).