Castle Bleck is a location in Super Paper Mario. It is seen in various intermissions between chapters in the game, where Count Bleck gives his minions their orders for the chapter. Castle Bleck is also the entire setting for Chapter 8.
Nastasia reports to Count Bleck that there has been interdimensional activity. Bleck suspects that the hero of prophecy has begun his destiny. Bleck sends O'Chunks to deal with him, and Dimentio also volunteers to help.
Unfortunately, O'Chunks has failed in his task, so Bleck sends Mimi instead. Nastasia goes to hunt down the unhypnotized goons of the castle. Meanwhile, Peach meets up with a Hammer Bro. and a Koopa Troopa, who decide to join her. The Koopa decides to find Bowser instead, while the Hammer Bro goes with Peach to find an exit. However, the Hammer Bro gets hypnotized by Nastasia, who attempts to do the same to Peach, but the princess is mysteriously teleported away.
Gloam Valley Interlude
Mimi returns, defeated by the hero. Bleck, running out of ideas, sends Dimentio after the hero of prophecy. Meanwhile, Nastasia is still searching for those minions and characters that have been left unhypnotised. Luigi finds two Goombas who trick him into helping them find an exit. However, it turns out to be a dead end and both Goombas are hypnotised, along with Luigi, who becomes Mr. L.
The Bitland Interlude
Bleck's third minion, Dimentio, also has been defeated by the hero of prophecy. Bleck has no choice but to send Mr. L after Mario.
With all 8 Pure Hearts in hand, Mario and Co head off to Castle Bleck to defeat the count and end the Dark Prognosticus and the Void before it ends the world as we know it. Mario and Co face familiar foes and Bowser's brainwashed minions. Bowser, Peach and Luigi come across O'Chunks, Mimi and Dimentio, with the three heroes ending up lost in the castle. Luigi discovers from Dimentio that he has been plotting against Bleck the whole time. Mario, meanwhile, heads to defeat Bleck. At first he has little success, but with the power of the Pure Hearts and the other three heroes, they manage to defeat him. Dimentio then fuses Luigi with the Chaos Heart to make Super Dimentio, who imprisons the count and Tippi in Dimension D with Bleck's other minions. Tippi and Bleck use their powers of love to reactivate the Pure Hearts, making Super Dimentio vulnerable to attacks. After Super Dimentio is defeated, Luigi gains control of himself and Tippi and Bleck leave to go pursue their love.