A Black Pit Bob-omb is a large, extremely powerful Bob-omb capable of creating an explosion powerful enough to create gaping pits, referred to as "black pits".
In The Super Mario Bros. Super Show! episode "Rolling Down the River / The Mario Monster Mash", Captain Koopa uses a Black Pit Bob-omb to create a black pit in a river; Captain Koopa does this to help him stall his opponent, Mark Twang, from beating him in a race to become King of the River.