WARNING: The following contains spoilers for One Piece Chapter #1021, "Demonio," by Eiichiro Oda, Stephen Paul and Vanessa Satone, available in English via Manga Plus and Viz Media.
In Chapter #1021 of One Piece, Luffy is ready to go up against Kaido again after being rescued from drowning -- and having some meat, of course. He's asked Momonosuke to turn into a dragon and carry him back up to Onigashima so he can face Kaido. However, Luffy won't be at his full strength this time, which could affect the battle more than he realizes.
Yamato has been fighting Kaido in Luffy's absence, using his Inu-Inu-no-Mi to turn into the guardian wolf spirit of Wano. This battle has taken a toll not only on Yamato, but Kaido as well, meaning Luffy will have a better chance at defeating the villain in round two of their fight. And if Yamato stays by Luffy's side, it could tip the scale in the Straw Hats' favor.
There's one additional factor that could help Luffy: Momonosuke has asked Shinobu to turn him into an adult. Using her Ripe-Ripe Jutsu, Shinobu can change Momo from a child into the adult he would have been had he not been sent forward in time. Momo believes if he's fully grown, it could affect his Devil Fruit powers and change his dragon form. Right now it's not much bigger than an average human, but being fully grown could increase his dragon size to be comparable to Kaido's own dragon form. That's not a guaranteed result but Momo insists on trying it -- if his plan works, it could be the deciding factor in Luffy's fight against Kaido.
Luffy has come back from the brink of death to face Kaido once again, but this time he has two allies who have personal vendettas against the Beast Pirate. Fueled by their desire to free Wano and avenge their fallen friends and family, they may have what it takes to help Luffy in the final hour to finally set the country free and open its borders. If Momonosuke's plan works, he could be able to combat Kaido's enormous dragon form while Yamato and Luffy try to finish him off.
There's no telling who else might show up for the final showdown against Kaido, so Luffy could have more help than in his first try. So while the One Piece protagonist won't be at full strength, he can combine his power with that of his friends to overcome the threat Kaido presents. Kaido's fall would mark a new era for Wano, and it would only be fitting if Momonosuke and Yamato -- who both represent Oden's legacy -- were a part of that new beginning.