Tubba Blubba

"I smell delicious ghosts! Open the door!"

- Tubba Blubba

Tubba Blubba is a monstrous blue Clubba and follower of Bowser who, despite his fearsome appearance, is actually somewhat sensitive and cowardly. His nickname is "The Invincible Tubba Blubba".

Paper Mario
Lady Bow mentions that Tubba Blubba was continually scared and bullied by the Boo inhabitants of Boo's Mansion and Gusty Gulch, who took great delight in frightening him. When Bowser obtained the Star Rod and imprisoned the Star Spirits, he made Tubba Blubba completely invulnerable by removing his heart from his body, apparently leaving a crudely stitched patch where it once was, and appointed him as guard of the Star Spirit Skolar.

No longer frightened by Boos, Tubba Blubba began taking vengeance upon them for ridiculing and frightening him, steadily devouring all Boos he came across, ironically making the Boos scared of him. Several attempts were made by brave Boos to discover some way to pierce Tubba Blubba's seemingly impenetrable defenses; most often, these Boos never returned from Tubba Blubba's Castle, but the rare few that did escape and learned at least a partial amount of Tubba Blubba's secret weakness were often tracked by the ghost devourer and eaten before they could reveal too much. Tubba Blubba's habit of devouring Boos and his inability to be injured earned him a sinister reputation, with even Bowser's own troops beginning to show fear of Tubba Blubba's might.

Mario first encounters Tubba Blubba during one of his Boo-devouring excursions on the outskirts of Gusty Gulch. After exploiting Lady Bow's Outta Sight technique to avoid drawing attention to himself, Mario follows the unsuspecting beast back to his castle and manages to gain access to his bedroom. Here, Mario finds Yakkey, an anthropomorphic key which unlocks the door to the Windy Mill, the storage place of Tubba Blubba's heart. Yakkey alerts its master to Mario's presence, initiating a destructive and harrowing chase through the castle that ends on the way to the mill, when Tubba Blubba's progress is impeded by a group of Boos.

Tubba Blubba breaks through this barrier while Mario is engaged in combat with his sentient heart. Upon its defeat, it flees from Mario and rejoins with its body, which makes Tubba Blubba feel invincible but actually physically weakens him. After his defeat, Tubba Blubba, with tears in his eyes, reveals that he is actually quite sensitive and begs for forgiveness before releasing all of the Boos he had consumed. He then retreats to his castle, claiming that he does not want to be invincible if it means fighting people like Mario. He is not seen again until the game's ending parade, during which three Boos give him a ride through the air while his heart chases after him.

Super Paper Mario
In Super Paper Mario, Tubba Blubba is mentioned as being the star of an anime based on him known as The Blubbening; it has run for at least three seasons. The Blubbening involves a princess and robots and also happens to be a favorite show of Francis.

Trivia

 * Tubba Blubba's name is a corruption of "tub of blubber" (indicating obesity) written in the style of the Clubba species' name.
 * Tubba Blubba can be thought of as somewhat similar to Sluggy the Unshaven of Super Mario World 2: Yoshi's Island, another character who is stated in-game to be invincible while actually having a weakness in the form of his heart. However, in Sluggy the Unshaven's case, the heart is not separate from but is protected by his gelatinous body.
 * Tubba Blubba's name sometimes appears on the score card in Mario Golf Toadstool Tour