*The Megahammer is one of Bowser Jr.'s robots appearing in Super Mario Galaxy 2. This robot can be found in Bowser Jr.'s Fearsome Fleet, a location at the end of World 3. It is fought on a ringed planet made of metal. After he is defeated, the Megahammer can be seen on the Starting Planet of Bowser Jr.'s Boom Bunker, this time broken. However, his Bill Blasters still work, which is necessary to bust open the cage on his right arm so Mario can use the Cannon to make his way deeper into the galaxy.
When the Megahammer makes his entrance, Bowser Jr.'s pod grows a mask and attaches itself to a robot body. This battle requires use of Yoshi. There are Yoshi eggs appearing around the ring. Megahammer releases Bullet Bills and Banzai Bills.
When the battle starts, Mario must gather Yoshi (if the former hasn't already) who can use his tongue to grab a Bullet Bill that can shoot at Megahammer's blue glass-like orbs to break it as an attack. Afterwards, Yoshi must gather a Bullet Bill with his tongue and shoot it at Megahammer. If not shot on an orb, it won't affect Megahammer. Sling Stars occasionally appear for Mario and Yoshi to shoot at the back of Megahammer instead of walking for a long time to reach the back. However, Megahammer will unleash a shockwave from his middle in retaliation. Megahammer's most powerful attack is a hammer slam which occurs only after one of his orbs is broken.
When Mario and Yoshi successfully attack all of Megahammer's blue glass orbs, Megahammer opens his head with glass on it so Mario can use Yoshi to get a Bullet Bill to shoot the glassy part twice when the robot performs his hammer slam attack to fully defeat Megahammer and to move onto World 4.
- In the Beta, Megahammer was originally called "Mighty Mattelloid" which is a combination of the words "Mallet" and "Planetoid" due to his strategy. This was seen in a Boy's Life magazine.
- The MegaHammer, in his attack patterns and the way you damage him, is similar to the Egg King from Sonic Rush. Both have weapons they can shoot to damage the player (Lasers for Egg King, and Bullet Bills for MegaHammer) and their primary form of attack is by slamming onto the ground with hammer like hands.
- Megahammer somewhat resembles Kululu from the Sgt. Frog anime.
- Megahammer also resembles both Mega AMP models from DK: Jungle Climber.