The Yoshi Bomb is an attack in the Super Smash Bros. series that Yoshi is capable of performing. It is basically a ground pound, and the developers rightfully gave this ability to Yoshi seeing that he is considered the originator of the now popular attack (in the SNES game Super Mario World 2: Yoshi's Island). It can be performed when the player controlling Yoshi presses down on the joystick, then the B button, which will cause Yoshi to quickly jump in the air and perform an earth shattering ground pound. Afterwards, two stars will surround him for a split second, which will harm any opponents to the right or left of him.
So far, the move has been seen in all of the Super Smash Bros. games.