Bomber is an enemy from the Kirby series. It resembles a missile-shaped bomb with legs and a skull painted on it's side. Bombers walk around until they reach a platform's edge, at which point they'll teeter over it, then fall off. When they land, they explode with a fairly decent range. If Kirby inhales it, he becomes Crash Kirby, a one-use ability that deals massive damage, destroying almost every enemy on screen.
Bomber appears in the Super Smash Bros. series as an item starting with Super Smash Bros. Ultimate. It is a throwing item, creating a large explosion when thrown. If none of the fighters touch it however, it will activate itself similar to a Bob-omb and wander the stage on it's own. Unlike a bob-omb if it reaches the edge of a platform it will teeter for a bit before falling off and exploding.
Prior to this it also appeared in Super Smash Bros. Brawl as a collectible trophy.