Okay, this one's a bit tricky because it’s not just a single chapter. Momo's big grown-up transformation is a process, not a one-and-done reveal. The real visual payoff—where he’s suddenly this massive, adult pink dragon fighting alongside the grown-ups—happens in Chapter 1025, 'The Three-Way Battle Royale'. That’s the iconic spread where Yamato sees him and asks Luffy if that’s his brother, and it’s just a fantastic moment of payoff after all his pleading to age up.
But honestly, the build-up is what makes it. You see him wrestling with the idea earlier, especially around Onigashima. The tension with Shinobu and her fruit's power is there for ages. The actual decision and the lead-up to the transformation get more focus in the chapters right before, like 1024. Skipping straight to 1025 kinda misses the emotional weight of a scared kid choosing to shoulder a burden he’s not ready for, even with magic aging fruit juice. The chapter's great, but it’s the culmination of his whole arc in Wano.