Tubba Blubba is the main antagonist of Chapter 3 in the first Paper Mario game. Tubba Blubba was responsible for eating many Boos.
He imprisoned Skolar, the third Star Spirit, inside his castle. He is said to be Bowser's strongest follower because Bowser made him invincible. He is often called "Invincible Tubba Blubba". If encountered in Tubba Blubba's Castle, Mario cannot defeat him and must run away. Mario soon discovered that a talking key named Yakkey unlocks the door at Windy Mill, where the secret to Tubba Blubba's invincibility lies. Yakkey woke up Tubba Blubba, however, and he chased Mario over to the doors of the castle where many Boos from a ghost town in Gusty Gulch held the doors shut on Tubba Blubba.
Mario reached the Windy Mill where he found Tubba Blubba's Heart, which was the reason for his invincibility. Mario fought Tubba's Heart, who ran away when he thought he was going to lose. He then reunited with his body, thinking it would make him stronger, but all it did was take away his invincibility and Mario easily defeated him. He gave back all the ghosts he ate and ran away crying. Afterwards, Bow revealed that he was eating the Boos as revenge for them scaring him all the time because he was such a coward.
In the credits parade (which is non-canon with the events of the game) Tubba Blubba is seen seemingly flying, but is really being carried by Boos, and Tubba's Heart is frantically chasing after his body.
Tubba Blubba's Heart
This is basically Tubba Blubba's heart except it can attack you and talk. Apparently when Tubba Blubba is separated from his heart he is invincible. The Heart has one of the most powerful attacks in the game, rivaling that of the attacks of The Master.
Bow is the best partner for the battle against Tubba's Heart, who has 50 HP, 6 ATK, and 0 DEF. Whenever he charges up for his ultimate attack, Mario should have Bow use Outta Sight. This is the only time she should use the attack because she can't do anything for the turn after she uses Outta Sight. Sometimes he may attack Mario for 6 damage. Once he's down to 5 HP or less, he will run away.
Boss Battle
The battle with Tubba Blubba, now that he isn't invincible anymore, is easy unless Mario has 6 HP or less, as Tubba Blubba has an attack power of 6. He has 0 DEF and 10 HP, so it will only take one or two turns to defeat Tubba Blubba, depending on what attacks are used.