The Forest Training Camp Arc has moments of these. The villains sent to deal with U.A.'s students manage to do more damage than the League of Villains before, and Chapter 75 ends with Midoriya using One For All at 1,000,000% on a villain.
The Hideout Raid Arc where All For One finally takes matters into his own hands. And when All For One moves, that means All Might himself gets personally involved as well. The results? Half an entire city gets itself wiped out from their clash alone. Note that both of them are severely weakened from their last fight, which really begs the question of just what the hell was their last fight like. If that's not all, All Might even goes way past his time limit (which reveals his true form for the whole world to see as well) and just keeps going by using One For All on his arms only. Between all of that, Nana Shimura, All Might's predecessor, is also revealed to be Shigaraki's grandmother.
Chapter 125, where we get our first look at Overhaul's power. Poor Magne.
The battle against Overhaul includes mind-blowing twists, such as Mirio losing his Quirk, Midoriya breaking through the wall to enter the fight and activating Full Cowl 20%, Team Ryukyu falling through the roof to barge in the fight with the last one of the Eight Bullets, Eri's power being awakened and being able to return things to a previous state, with her and Midoriya's powers combined they are able to use Full Cowl 100%.
In Pro Hero Arc, Endeavor using his ultimate move Prominence Burn on Hood Nomu in the sky, followed up Enji's raising his arm to claim victory in the aftermath, just like All Might.
In Joint Training Arc: Deku's activating his new quirk "Blackwhip" by accident during final part of Joint Training Battle. Later it's revealed it's only ONE of his six new quirks.
Meta Liberation Army arc has the flashback, withShigaraki as young Tenko Shimura accidentally killing his family and his dad on purpose Patricide with Slasher Smile, manifesting his quirk at the worst possible moment.
The Paranormal Liberation War Arc includes many of these moments, such as the deaths of multiple named pro heroes, Hawks actually killing Twice, Dabi revealing himself as Toya Todoroki and revealing Endeavor's abuse of his family to the public, Best Jeanist reappearing after having disappeared for months, Mirio getting his Quirk back and All For One taking control of Shigaraki.
Chapter 362 massively shocked almost every manga reader in its final panel, which shows Bakugo, laying lifeless with a massive, gaping hole where his heart is. This scene set the internet abuzz with conversation, despite it only being a Disney Death that gets undone a few chapters later.
