Bowser is in his Koopa Clown Car, which will have a pair of arms and claws on it. The battle takes place on the rooftop of Bowser's Castle.
Bowser will attempt to smash you with the claws on his clown car. Before the player can even damage Bowser, they will need to destroy the claws on the clown car. This is done by ground-pounding the back of each claw twice. After this is done, the second part begins.
Now the player can damage Bowser. To do so, they need to wait until Bowser pounds the ground with his clown car. He will stuck in the ground for a short time. The player will need to quickly ground pound Bowser's head. After the player does this once, Bowser will throw Bob-ombs at Mario that explode shortly after thrown. He will also shoot fireballs and unleash fire beams with his clown car. He will still do his ground pound, so the player can still damage him. Ground-pound his head 3 times, and Bowser is defeated.