Bowser In The Fire Sea

Bowser in the Fire Sea is the second Bowser level, which appears in the Castle Basement. It is unlocked after clearing the Boarding Bowser's Sub mission in Dire, Dire Docks. It is a linear level with platforms on top of a large lava plane. At the end is the second Bowser boss fight, which unlocks the Second Floor of Princess Peach's Castle.

Blargg
The unused Blargg enemy is referenced to appear in Bowser in the Fire Sea.