One of the strangest fights in Dragon Ball Z is the battle between the composite warrior Gotenks and the upgraded form of Majin Buu, colloquially known as Super Buu, after Evil Buu consumes his more innocent counterpart. While the first portion of the fight is largely dominated by Gotenks' patently bizarre special attacks, Gotenks shocks Buu by transforming into a Super Saiyan 3, leading to a genuine battle for the fate of the universe that comes to an abrupt end by the Fusion Dance combining Trunks and Goten wearing off before Gotenks can deliver the final blow. However, this leaves open the question of whether Gotenks was actually stronger than Super Buu or if the supervillain secretly held the upper hand the whole time.
Shortly after Gotenks' fusion wears off, Super Buu is confronted by Gohan after the young Saiyan recently received the ultimate power boost from the Elder Kai. Buu reveals to Gohan that he was aware that Gohan survived his initial battle against Buu's previous battle all along, sensing Gohan steadily growing in power as the Elder Kai performed the admittedly odd ritual to awaken Gohan's latent potential. Buu claimed he was simply biding his time by humoring Gotenks and prolonging their own fight as he waited for Gohan to complete his ascension and return to Earth from the Supreme Kai's world. However, Buu may not be completely telling the truth about the circumstances of his fight with Gotenks.
While Buu clearly underestimated Gotenks throughout much of their battle, there were several instances where it appeared that the fused fighter actually inflicted genuine damage on Buu over the course of the showdown. From the Super Ghost Kamikaze Attack damaging Buu to Gotenks and Piccolo nearly incinerating every bit of Buu in the Hyperbolic Time Chamber before Buu managed to reform good as new, Buu was on the ropes several times. Moreover, when Gotenks reached Super Saiyan 3, Buu appeared legitimately concerned as Gotenks began powering up a massive Kamehameha Wave to destroy him for good -- only for Gotenks to run out of energy and transform back to normal moments before his fusion wore off.
Gotenks certainly got some good shots in on Buu, and the villain may have been poised to pay the ultimate price for not taking the composite warrior more seriously... but the fact of the matter is that Buu wasn't taking the fight seriously for the majority of its duration. Visibly bored by Gotenks' childish antics, it wasn't until Gotenks turned Super Saiyan 3 that Buu began genuinely engaging his opponent. Had Buu been taking the fight seriously from the start, the pink villain may have proven more than a match for Gotenks, even with the hero transformed as a Super Saiyan 3, not allowing Gotenks to inflict those successful attacks in the first place.
Gotenks is certainly one of the strongest fighters in the entire Dragon Ball franchise, and one of only two warriors to canonically achieve Super Saiyan 3. However, it wasn't until the very end of Buu's battle against Gotenks that the villain appeared to feel pressured by his opponent, shrugging off Gotenks' previous attacks. Gotenks hasn't played a major role since his epic fight against Super Buu, outsmarted by the villain shortly thereafter, and the fused warrior may have simply not had what it took to put Buu down. Gohan truly came at the nick of the time to save the day from Buu, with not even Super Saiyan 3 Gotenks able to win the fight once Buu got serious.
