Who is the strongest version of Majin Buu in Dragon Ball Z? His final form may have been Kid Buu, but that wasn’t the height of his power.
A common misconception regarding Dragon Ball Z’s final villain is that Kid Buu was Buu’s strongest form, but that’s actually not the case. Kid Buu was the last version of the character that the Z-Warriors had to face, but he had other forms that the heroes had to fight as well, beginning with the most well-known incarnation of the character, who is simply called Majin Buu. There’s also Evil Buu and Super Buu. In Dragon Ball Z’s final episode, Goku met Uub, a good, human reincarnation of Kid Buu.
The evil entity known as Buu gave the Z-Warriors one of their toughest battles in Dragon Ball Z. Once he was unleashed, he engaged in separate battles with Goku and Vegeta. After splitting into good and evil sides, the Evil Buu absorbed his good half and completed the transformation into the much more powerful Super Buu. Following guidance from Piccolo and Goku, Goten and Trunks were able to fuse into Gotenks and battle him in their Super Saiyan 3 state. Unfortunately, even they couldn’t take him down and were eventually absorbed. The same happened to Ultimate Gohan. Later in the saga, Goku and Vegeta were able to free the people Buu had absorbed, causing him to enter his Kid Buu form for the final confrontation with the Z-Warriors.
Due to his chaotic and pure evil nature, Kid Buu was shown to be Dragon Ball Z’s most dangerous villain yet, as he did what no one else had done before and blew up the Earth. Even so, this wasn’t his most powerful state. Buu was at the height of his power when he – as Super Buu – absorbed Ultimate Gohan. After unlocking the Ultimate form, Gohan was once again the anime’s strongest hero, above both Goku and Vegeta. Gohan was able to overpower Super Buu but was outmatched when the villain absorbed Gotenks and Piccolo. When he too was absorbed, Super Buu seemed nearly unbeatable.
Due to the power-ups, he received from Gohan and Gotenks and the boost to his intelligence he gained from Piccolo, Super Buu was stronger than ever. It took the power of Super Saiyan Vegito (the Potara fusion of Goku and Vegeta) for Super Buu to be sufficiently challenged. By comparison, Kid Buu was much weaker. It was shown that he was about on par with Super Saiyan 3 Goku, who couldn’t finish him off due to the limitations of the form.
It’s important to keep in mind that though Kid Buu was the Z-Warriors’ last challenge, he wasn’t their strongest opponent in Dragon Ball Z. The reason why he was so difficult to beat despite being weaker, and why it took a Spirit Bomb powered by the people of Earth to destroy him, is explained by the loss of their greatest assets: Ultimate Gohan and the Potara Earrings. Goku and Vegeta were forced to find a way to beat Kid Buu without fusing and without Gohan on their side.