Majin Buu, or Buuhan as he's known after absorbing Gohan, is the most powerful villain to appear in Dragon Ball Z. Even though Kid Buu is the arc's final villain, Buuhan displayed much more power in his limited screen time. Buuhan possesses overwhelming strength, martial arts expertise, and the ability to heal all his injuries. His increased intelligence, obtained from Gohan and Piccolo, also helps set him apart from his rampaging toddler counterpart.
Unfortunately, along with Gohan's power, he also absorbed the teen Saiyan's post-Cell uselessness syndrome. Buuhan appears in six episodes, spending four of them being ground into a pink pulp by Vegito.
Buuhan's first appearance comes at the end of Episode 267 when he successfully absorbs Gohan, and soon uses his new and improved strength to effortlessly overpower Goku and Vegeta. The mighty Saiyans are helpless, landing only one weak blow between the two of them. Buuhan quickly gets bored and decides to kill them rather than showboat.
However, Episode 269 is when Buuhan's grand one-and-a-half-episode reign comes to an end. Goku's and Vegeta's fused form, Vegito, finds immense joy in humiliating the villain. Buuhan's confidence and composure are directly tied to how the battle is proceeding. Still, he manages to throw temper tantrums and give delusional monologues in between beatings.
Buuhan's anger appears to decrease his intelligence as well, as he seems unable to speak in complete sentences. He almost becomes sympathetic with Vegito wailing on him so mercilessly. Eventually he snaps, and his anger begins to tear apart the very fabric of the universe. Dende confirms that Buuhan could end all of reality if left unchecked. Yet nothing comes of it as this potential disaster is soon averted with one swift punch from Vegito.
Like most of Dragon Ball Z's villains, Buuhan manages to stay alive due to the hero's arrogance. However, he's also different thanks to his ability to regain his composure after realizing he's outmatched. Once Vegito puts a stop to his universe-destroying outrage, Buuhan acknowledges that he is the weaker fighter. In Episode 271, Buuhan demonstrates what truly makes him dangerous. Accepting that he cannot overpower Vegito, he begins trying to outsmart him with far more bizarre techniques.
Once Buuhan successfully transforms Vegito into a piece of candy, his own arrogance gets the better of him as he celebrates instead of finishing the job. This mistake takes him from the show's strongest villain to its biggest joke. He gets so thoroughly pummeled by the tiny Candy Vegito that he actually chooses to restore the fused Saiyan to his normal state.
To call Buuhan a disappointment would be an understatement. Granted, Frieza and Cell also received humiliating beat downs, but Buuhan's was different in that it was played for laughs. He is the most emotional, yet calculating, villain ever encountered but it amounts to nothing here. Buuhan didn't kill anyone or harm the Earth in a significant way. Even the initial beating Goku and Vegeta received was relatively minor, all things considered. Buuhan is easily the most powerful villain in all of Dragon Ball Z, yet he leaves behind no legacy after losing this form.
Majin Buu was a fascinating concept for a villain. Not only can he steal people's powers, but he can steal their knowledge as well. This ability gives Buuhan reality-threatening strength, a cunning mind, and intimate knowledge of Dragon Ball Z's heroes. These traits should have made for an iconic villain. Instead, he spent two-thirds of his screen time screaming and flailing angrily while receiving the spanking of a lifetime.