From WiKirby, your independent source of Kirby knowledge.
Bomb-Bomb is a Power Combo of two Bomb abilities in Kirby 64: The Crystal Shards. It allows Kirby to fire missiles from his mouth, up to three if they are charged. The missiles home in on the nearest enemy when launched, or fly in a straight path if no enemies are in range. Once three missiles are prepared, they will fire automatically, so Kirby cannot hold on to them indefinitely.
Bomb is one of the few powers that does not simply make a bigger version of itself when combined with itself. While the missiles will attempt to home in on enemies, they are notoriously bad at turning, meaning that they will more often than not make circles around the intended target.
Like the other abilities in Kirby 64: The Crystal Shards, this ability does not change Kirby's physical appearance in any way.