Megahammer

Megahammer is a boss in Super Mario Galaxy 2, which appears at Bowser Jr.'s Fearsome Fleet. It is a giant robot operated by Bowser Jr., which vaguely resembles a Koopa Clown Car.

It attacks by launching Bullet Bills and Banzai Bills. It also features a shockwave attack. To defeat it, the player must use Yoshi to catch the incoming Bullet Bills with his tongue, and spit them back at the robot's three blue orbs, two of which reside on its chest, while the last is found on its back. Players can use the Sling Star to get to the other side faster instead of walking around Megahammer. Once all 3 orbs are destroyed, the protection on Bowser Jr's control in the robots head. When Megahammer slams down it's mallets, the player must use a bullet bill to hit Bowser Jr's cockpit twice.

Megahammer is fought twice, with the second fight being under the Daredevil Comet conditions.

Later in the game, Megahammer can be seen in Bowser Jr.'s Boom Bunker broken. The Toad Brigade is seen when first in the galaxy, hiding behind an arm. Megahammer is still alive, because Bullet Bills are shooting out of it, and its eyes are blinking black to red.

Trivia

 * Megahammer was originally going to be called Mallettoid, a pun on "mallet" and "metalloid", but this was changed before the final version of the game.
 * It is unknown how Bowser Jr. destroyed Megahammer, yet one can imply that he used his Boomsday Machine, as Megahammer remains are in the level where Mario battles the Boomsday Machine.