Akira Toriyama's Dragon Ball franchise has long revolved around periodic World Martial Arts Tournaments. However, the first friendly competition in Dragon Ball Z took an unexpected turn. The 25th World Tournament was disrupted by Babidi sending his agents Yamu and Spopovich to steal energy to awaken the villainous Majin Buu, along with the Supreme Kai and his attendant Kibito aiming to recruit the Z Fighters to stop them. This resulted in many fighters leaving prematurely to save the universe once again, with the remaining contestants engaging in a battle royale-style finale.
Here is how the tournament might have gone had Yamu and Spopovich, along with Supreme Kai and Kibito, not intervened and revealed their true intentions. Keep in mind that the tournament revolves around single-elimination one-on-one fights, with contestants eliminated by forfeiture, knockout or ring-out -- lethal force results in immediate disqualification.
The First Round
The first set of fights from the opening round were already revealed: Krillin easily defeated Pintar while Videl was brutally beaten by Spopovich. Some of the other fights in the round are similarly simple to predict: Trunks and Goten (disguised as Mighty Mask) would best Killa while the Babidi-empowered Yamu would defeat Jewel. The outcomes of other fights are hinted at: Piccolo would likely still be beaten by the Supreme Kai. Gohan, visibly surprising Kibito with his Super Saiyan 2 transformation, would emerge triumphantly.
In the original tournament, Android 18 deliberately threw her fight against Hercule Satan after he promised her a fortune even larger than the prize money so he could maintain his reputation with the public. With Mr. Satan's victory no longer a guarantee, 18 is more likely to defeat him for a better chance at a payout.
The biggest question is who would win that first round match between Goku and Vegeta. While both Saiyans had been training diligently for seven years since the Cell Games, it took Babidi's magical empowerment to create Majin Vegeta and give the Saiyan Prince a fighting chance. And even without the magical upgrade, Goku secretly was holding back in his duel the entire time by not revealing the Super Saiyan 3 form, meaning Goku would likely triumph over his longtime rival.
The Quarter Finals
The four quarter-final matches are when things become much more interesting. Just as the Supreme Kai would beat Piccolo, he would have an even easier time confronting Krillin. Against Spopovich, Gohan would finally get revenge for his brutal beating of Videl and knock him out with full Saiyan fury. Mighty Mask (Trunks and Goten) would similarly defeat Yamu, eliminating the last of Babidi's representatives in the tournament.
The biggest fight of the quarter-finals would be between Goku and Android 18, with the synthetic fighter finally getting to experience a showdown against the target she was originally designed to kill by Dr. Gero. While 18 boasts unlimited energy, the training Goku experienced in the afterlife would give him an edge, scoring by ring-out.
While Goku would likely sense that Mighty Mask are disguised Goten and Trunks, with the young duo probably forced to transform into Super Saiyans just to keep up, he would still humor them in a fight. Given the constrictive disguise, the boys wouldn't be able to fight to their full potential and would ultimately be defeated by Goku.
The biggest fight in the semi-finals -- Gohan and the Supreme Kai -- could go one way or the other. However, the Supreme Kai was shown to be continually surprised by how strong Saiyans had grown as he worked with them against Babidi, even going as far as conceding to Goku when the warrior threatened him to stand down so he could proceed to fight against Majin Vegeta. With that in mind, Super Saiyan 2 Gohan may well triumph over the Kai.
The Final Round
With Gohan emerging triumphant from the semi-finals, a final round Dragon Ball Z's 25th World Martial Arts Tournament would all come down to a sparring match between father and son: Goku and Gohan. Gohan is a formidable fighter in his own right but he's let his training fall by the wayside, while Goku has spent the past seven years doing some of the most rigorous training of his entire life.
Goku is more likely to use the final round of the tournament as a glorified martial arts lesson for Gohan, demonstrating how to tap into his latent potential while reminding him of the importance of keeping up with his training. And with Goku returning to the afterlife following the tournament, rather than beating his son down in the ring, he's more likely to cede victory to Gohan once he's given him one last lesson.