Mushroom Kingdom

Mushroom Kingdom is a world that appears in all the Dark Storm Storm games. It is confirmed to re-appear in DS3. It is from the Mario game series. The ruler of this world is Princess Peach

Dark Storm
Stephen arrives here after Bikini Bottom is sealed. Mario is fighting Bowser, and Strephen assits. After being defeated again, Bowser runs into his castle, leaving Stephen to explore the world. After entering Peach's Castle, Princess Peach greets Stephen, but tells him of Bowser's intentions to take the Realm of Creativy for himself! Mario and Stephen decide to infiltrate Bowser's Castle, but the Koopalings, having spied by hiding, tell Bowser what the plans are. Suddenly, Bowser jumps to the top of his castle, followed by the CDS (Castle Defense System) Darkness! After a violent battle, the CDS explodes, and the castle blows up along with it! Bowser is long gone, though, and the core is revealed! After the core is sealed, Stephen leaves.

First Visit
Mushroom Kingdom and Tri-State Area switch places. The world is split into four rooms, and only Peach's Castle's explored. Stephen arrives in the Dining Hall, and meets up with Mario again, while Bowser is plotting his revenge. Stephen then goes into the Throne Room, where Princess Peach is waiting for him, but the reunion is short when the CDSR(Castle Defense System's Revenge) Darkness attack the castle! After a long battle, the CDSR falls, and the core is revealed and sealed.

Second Visit (optional)
After completeing Tri-State Area, Stephen returns and finds out that Shroobs have overrun the castle. Stephen goes to the Shroob Throne, where he fights Princess Shroob, but Princess Shroob doesn't die! When the shroobs flee, Stephen saves Princess Peach from a death trap and leaves.

Trivia

 * It switches places in DS2 with TSA because fans liked Mushroom Kingdom better
 * The CDS is the second-largest boss Darkness, being topped by the End Of The Line
 * ? blocks can be found in Dark Storm, one gives Stephen the first emblem piece for the Alpha + Omega charm