Bowser in the Fire Sea

Bowser in the Fire Sea, also simply called the Fire Sea, is the second Bowser level in Super Mario 64 and Super Mario 64 DS located in the basement of Mushroom Castle. This level is made of concrete and mesh platforms above a huge lake of lava. Several Bullies and Goombas guard these platforms and the route to Bowser's arena. This level is unlocked by completing Board Bowser's Sub in Dire, Dire Docks, and its own completion unlocks Snowman's Land, Wet-Dry World, Tall Tall Mountain, Tiny-Huge Island, and Chief Chilly Challenge (DS only, supposing that both the Power Caps and Luigi are both unlocked).

The entrance to Bowser in the Fire Sea is found in the same room of the Mushroom Castle as the entrance to Dire, Dire Docks, which requires 30 Power Stars to enter. Before the player obtains the first Power Star from Dire, Dire Docks, the blue portal to the water level will be in front of the entrance to Bowser in the Fire Sea. Once the first Power Star of Dire, Dire Docks is obtained, the blue portal will move to the back of the room, allowing access to Bowser in the Fire Sea. One Power Star can be found in the Nintendo 64 version of the game, while two can be found in the Nintendo DS remake.

Layout
The player starts on a small platform with a metal platform near it. Stepping onto the metal platform will cause it to move. At certain points, the platform will dive under the lava, so the player needs to jump to nearby tilting platforms in order to avoid taking damage. After the moving platform's stopping point is a series of blue platforms that constantly go under the lava, then resurface. Beyond those is a Bully followed by three Goombas situated around a Spinning Heart. A raising pole, circled by an Amp, will help the player reach the tilting platforms above, and the pole at the end of those leads to a cage with an elevator that brings the player up to the next level.

The second level first contains a moving platform that goes through a flamethrower, which leads to a sloping mound. After the slope is a hanging grate the player can use to climb to the other side of the lava pool. Beyond that are two moving platforms, followed by a couple of Bullies, and a tall set of moving interconnected platforms with a Keronpa Ball that will lead the player to the next level.

The final level starts with a stone slope, containing a flamethrower, a Bob-omb, and a ! Block. After the stone slope is a row of sinking and rising platforms that are protected by flamethrowers and Amps. Beyond those is a stone structure containing rising and falling poles. Finally, a falling bridge leads to the warp that sends the player to the Bowser fight.

Bowser Battle
The tactic to defeat Bowser is the same as the fight in Bowser in the Dark World, though he has some additional moves. Bowser will immediately start the battle by jumping up and landing, making the stage tilt toward him. The same will happen if the player throws Bowser off the stage but misses a bomb, causing Bowser to land and cause the stage to tilt. Bowser can also warp to a different spot if the player is close, and charge at the player if they are far away. Throwing Bowser into a bomb will defeat him, granting the player the key to the castle's upper floors.

Missions
Two Power Stars can be collected in this course, with one being exclusive to the DS version of the game.

Star 1
Like in Bowser in the Dark World, there are eight Red Coins to be collected. The Power Star will appear atop a wall shortly before the warp that leads to Bowser himself. Wall-jumping is required to reach it.

Star 2 (DS only)
Near Star 1 is a Star Switch. Upon the player pressing the switch, the Power Star will appear on the far side of a lava pool that the player must quickly backtrack across in order to reach it before it disappears. If played as Luigi, the player can spin over the lava to the Star.