The Fiery Stronghold

The Fiery Stronghold is the only mission of Bowser's Star Reactor in Super Mario Galaxy. The mission's objective is to defeat Bowser.

Layout
The player begins in a Warp Pipe-like structure with a couple of Fire Bars and a Luma. Moving along the multicolored path, the player will reach a stone structure with Fire Bars, a Fire Pressure, and a Thwomp. Behind the Thwomp is a side-scrolling area where gravity is determined by where arrow directions. By avoiding the Fire Bars, black holes, and a Thwomp, the player reaches a circular platform with Fire Bars in an "X" formation. The path ahead winds around a stone tower and has many Thwomps, Fire Bars, and Fire Pressures. When the player reached a certain point on the tiled platforms, Bowser appears and begins firing meteors, attempting the break apart the platforms as the player climbs up. Additionally, on one of these platforms is a Life Mushroom. Once the player reaches the top of the tower, Bowser begins a dialogue, and the boss battle starts soon after.

At the end of the dialogue, Bowser sends him and Mario to a small planetoid above. Bowser attacks by jumping into the air and landing where Mario is standing, causing shockwaves to form upon landing. If the player can get Bowser to land on one of the blue areas, it shatters and Bowser burns his tail on the lava underneath, which causes Bowser to start running around the planet. By catching up with him, Bowser turns around and the player has to spin into his tail, which flips Bowser over. Spinning into him once more damages him and starts the next phase.

The second phase starts with Bowser shooting fireballs, followed by jumping and sending out two shockwaves. He then attempts to jump on Mario once more. After spinning and flipping him over, this time Bowser starts moving across the planet. Spinning into him once more starts the final phase. The third and final phase begins with Bowser shooting out more fireballs and shockwaves than last time. Afterward, he attempts to land on Mario again, though he runs and spins faster than the previous phases. Additionally, the player has to spin into Bowser twice when he is flipped over. After defeating Bowser, he and Mario fall back down to the tower and Bowser disappears, leaving behind the Grand Star.