Bowser's Star Reactor

Bowser's Star Reactor is a level located in Super Mario Galaxy and the first level where Mario fights Bowser. Before Mario fights Bowser, he has to travel through a short level that resembles one of the Bowser levels from Super Mario 64 (the music is also the same from those levels).

After Mario passes, Bowser will come down at start breathing fireballs at the platforms that Mario is on. This causes the platforms to start breaking and Mairo then has to go from platform to platform before they break. After a while he reaches the stage where Bowser is on. Bowser laughs and the gravity of the planet above them pulls them up.

Mario fights Bowser on this planet and after he defeats Bowser, the king of the Koopas mentions that he is not defeated yet. Bowser then uses some sort of magic to disappear. Bowser leaves a Grand Star behind, which Mario gets.