When used, he smashes straight downward into the ground, releasing a star on either side, which provides minor protection against nearby enemies. If used on the ground, Yoshi will jump forward before dropping down. The aerial version is a stall-then-fall move. This move can be canceled by grabbing the ledge while dropping. The Yoshi Bomb is capable of inflicting some serious shield pressure, and can also break a near-full shield.
This move's drop deals 18% damage in Super Smash Bros., while the stars produce 3% each. In Super Smash Bros. Melee, the Yoshi Bomb was slightly weakened in damage, with the stars only dealing 1%, but it still inflicts powerful knockback. In Super Smash Bros. Brawl, the attack was further weakened, but the grounded version now possesses a weak, fixed-knockback hitbox during the jump that links more successfully into the second hit. In all games, the stars can be reflected and absorbed. In Super Smash Bros. 4, and in a similar fashion to Bowser, the grounded version has the potential to break an almost-full shield if all of its hitboxes connect. However, like Bowser, the opponent can roll out of the way.
In the original Super Smash Bros., the move is called "Hip Drop" by Yoshi's in-game character profile, which was the standard name for the maneuver in the Mario Party series at this time; elsewhere in the Mario and Yoshi series the move is known as "Ground Pound". However, the move is listed as "Bomb" in the instruction booklet for Super Smash Bros refers to the move as simply "Bomb", which is likely an error; this causes it to share a name with special moves of Link and Samus, both of which coincidentally are also down special moves.
The move was then named as the Yoshi Bomb in Melee, Brawl, and SSB4. This is a bit of an unsubstantiated choice; no move has ever been known as "Yoshi Bomb" in the Mario or Yoshi series, and the Japanese name for the move remains ヒップドロップ (Hip Drop). In most in-depth Japanese sources, Luigi's new down throw in SSB4 also shares this exact name which implies that it's the exact same technique.
Special Move customization was added in Super Smash Bros. 4. These are the variations:
The move has become a somewhat standard move in Mario and Yoshi games, originating in Super Mario World 2: Yoshi's Island where Yoshi could use it to pound down stakes, crush crates, slam through soft dirt, and of course, damage and defeat enemies. Yoshi's animation during the midair descent is modeled after the Ground Pound from Yoshi's Story.
The stars emitted from the Yoshi Bomb are original to Smash Bros. Alternatively, as many mechanics of the Smash Bros. series are derived from the Kirby series, it's possible that the stars are a reference to how a great deal of ground-smashing attacks produce stars on impact, which Kirby can suck up and spit out.
The Japanese name for Yoshi Bomb on the other hand (Hip Drop) is a common alternate name for this type of move in several of the Mario and Yoshi-based games alike.