Egg Throw is Yoshi's Up B move in all three of the smash installments. Yoshi launches an egg upwards in an arc, which can be angled along a variety of trajectories, hitting anywhere from far horizontally in front of Yoshi to slightly behind and above Yoshi. The egg explodes upon contact or after moving along for a set air-time. Yoshi's Up B is fairly unique in that it is not a triple jump, does not noticeably aid in recovery, and does not put Yoshi into a state of helplessness. In SSBB, this is changed, and it does help with recovery. Even in Brawl, this move does not make Yoshi helpless.
Starting in Super Mario World 2: Yoshi's Island, Yoshi would eat enemies to turn them into eggs and then throw the eggs at other enemies. The explosions of the Eggs seen in Super Smash Bros. Melee and Super Smash Bros. Brawl are based on Yoshi's Egg toss in Yoshi's Story where the Eggs had larger explosions the happier Yoshi was.