Dragon Ball Super: Broly is about to bring the topic of fusion right back to the forefront, as the film introduces Gogeta into canon, and gives him a Super Saiyan Blue upgrade. Well, thanks to a new breakdown in Weekly Shonen Jump, we now have a lot more clear indication about how the various forms of fusion that create Vegito or Gogeta actually compare, in terms of power.
Here's the official breakdown:
"Here is the difference between “Potara” and “Fusion”!! “Potara” and “Fusion” both create super warriors! At first glance they look like similar ways of merging!! We’ll inspect their differences by comparing Vegetto with Gogeta (the one who defeated Janenba)!!!
Fusion: A symmetrical transformation pose!! The two who will merge must perform the same transformation poses as if reflected in a mirror!! During this time, if they mess up these poses even a little bit then they will become too fat or skinny!
Potara: You just have to put on an earring!! One person just puts a Potara on their left ear, and the other person puts the remaining Potara on their right ear!! The two are drawn together by the power of the Potara and combine into one!
Fusion: Their battle clothes are all the same! Everyone wears the same clothes after merging!! It turns out that these clothes are the native garb of the people of Planet Metamor, who taught Goku the Fusion technique!! Toriyama-sensei came up with this idea!
Potara: Whoa! Their clothes merge!! The clothes the two are wearing merges, too?! The gloves and boots are the same ones Vegeta had on! The main outfit is the same design as Goku’s outfit but a different color!!
Fusion: Requires similar people!! Only two people of very similar power and size can merge!! However, after thirty minutes they split back up and return to normal! Even so, they can merge any number of times!!
Potara: So good you can use it with anyone!! The Elder Kaiōshin accidentally merged with an old witch!! In this way, anybody can merge together with the Potara! However, you can only merge once in your life, and never return to normal!!1
Gogeta: Ultimate power united in body and soul!!
Vegetto: Their power is amplified!!"
The final tagline sums up the comparison in some grandiose words, but here's the main takeaway: Fusion is harder to pull off, and last a much shorter time than Potara, but the power that is achieved is much, much, greater. However, Potara is also supposed to come with the ominous catch that it is permanent - a rule that both Dragon Ball Z and Dragon Ball Super have managed to circumvent, when it comes to Goku and Vegeta merging into Vegito.
Understanding these finer points of Dragon Ball fusion is going to be important, as Dragon Ball Super: Broly will have Gogeta take on the limitless might of Broly. That battle could ultimately boil down to time: can Gogeta stay fused (even with a SSB power boost) for as long as it takes to bring Broly down.
Dragon Ball Super: Broly officially releases in Japan this December, so fans will get to see more of Super Saiyan Blue Goku in action soon enough. Funimation will be bringing the film to theaters in the United States on January 16. Dragon Ball Supercurrently airs its English dub on Adult Swim during the Toonami programming block Saturday evenings at 9:30 p.m. It is also available to stream on Funimation and Amazon Video. The Japanese language release of the series is complete, and available to stream on FunimationNOW, VRV, and Crunchyroll.