|Appearance||Super Smash Flash 2|
As expected, it is mostly covered in lava and it can damage players that fall on it. Unlike lava from Phase 8, lava in Bowser's Castle always stays at one level and never rises. The stage itself is comprised by three platforms: on the left and right of the stage are two platforms divided in three and two portions, respectively, that rise from the lava, this portions indicate where a Thwomp will randomly fall at high speed towards them and smash the platforms, sinking the portion and exposing the lava below. Any player crushed by the Thwomp will get damaged and will be launch far enough to be KO'd even at low percentages opponents, if players stand on top of the Thwomp as it ascends after falling, they will also be KO'd. In the center is a small platform which players can fall through into the lava but is a safe spot from the Thwomp.
Lava Bubbles, Firebars and the iconic bridge and ax from Super Mario Bros. appear in the background.
- The main track is a remix of the Bowser's Castle from Super Mario World.
- The alternate music track is titled Bowser's Rampage, which mixes Bowser's Castle Theme from Mario Kart 64 with many variations of Ultimate Bowser from Super Mario 64.
This stage is banned in competitive play. The boundaries are all extremely close to the stage, allowing for very early KOs, especially for characters with high base knockback on their attacks. The lava prevents bottom KOs, removing a lot of the offstage/edge game dynamics while providing a cheap means to extend combos or even KO opponents. The main platform is divided in two, encouraging campy playstyles as it is difficult for most characters to approach from one side to the other.
Bowser's Castle is a recurring area that makes numerous of appearances in the Mario series, usually serving as Bowser's stronghold, containing various obstacles which Mario must conquer before facing Bowser. It first appeared in Super Mario Bros. as the final level of the game, elements like the lava and the eye candies from the background: Lava Bubbles, Firebars and the bridge, also debuted in that game. Thwomps debuted in Super Mario Bros. 3 and are mostly found in fortresses and Bowser's Castle itself at the end of the game. The stage takes mostly the aesthetic seen from castle levels from Super Mario World, this is more evident with the music and the background.
- When a character uses a move with super armor above the lava; they will fall through the lava, depending on how long the Super Armor last, and KO themselves. The same goes for when a character has invincibility frames.