The following contains spoilers for My Hero Academia Chapter 356, "Regarding the Enemy" by Horikoshi Kohei, Caleb Cook and John Hunt, available now in English from Viz Media.
My Hero Academia's All For One is one of the most terrifying villains in any manga. Even when matched against Endeavor and Hawks, the highest ranking heroes, he was more than holding his own and felt comfortable enough in the heat of battle to make light of the duo's shortcomings. All For One displayed the strength and cunning that made him the most dangerous villain for decades but, in a surprising turn of events, is currently closer to defeat than he's ever been.
It seemed the titanic battle would be an easy win for All For One at first. Endeavor and Hawks fought their hardest, but the villain took an early lead when one of his taunts shook Endeavor enough for All For One to inflict a flesh wound. Fumikage Tokoyami and Kyoka Jiro attempted to fill the gap left by the Number One Hero and had limited success.
It took all of Tokoyami and Hawks' agility to escape All For One's attacks, and even that wasn't enough to escape unscathed. None of their own attacks seemed to be having any effect, and it seemed only a matter of time until the stalemate broke. It did eventually, however, when All For One's Quirk did the unthinkable and actively started working against him.
Before the villain knew what was happening, the battle's tide had completely turned. For every attack he tried to launch, he faced internal resistance from the Quirk factors he had stolen and was attempting to use. He deduced that this anomaly had risen because his version of the All For One Quirk was a synthetic copy of the one he'd passed to Shigaraki Tomura, but this knowledge alone couldn't help him regain control. Even his sensory Quirks, his sole method of observing his surroundings, refused to alert him to the surrounding dangers.
Realizing their opening, MHA's heroes wasted no time in beginning offensive strikes. Hawks hit him with a blow that finally cracked All For One's helmet, but it was Tokoyami's Abyssal Black Body Fleeting Blow that really destroyed it. Undaunted, All For One managed to wrestle control over his Rivet Stab Quirk, intending to finish them all with an indiscriminate strike. His plan was foiled by none other than Endeavor, who'd finally risen out of his stupor and bathed All For One with a sea of flames for good measure.
Without a regenerative Quirk and the cushion of his numerous durability boosters, it seems All For One might be beaten in a shorter time than the heroes expected. His defeat would be a boon for the heroes but wouldn't immediately win the war. All For One still has a part of his consciousness residing in Shigaraki as insurance, so he wouldn't be completely vanquished. He is highly unlikely to give up his main body without a fight though, and it wouldn't be surprising if his body itself was somehow booby-trapped. Whatever the case, this certainly isn't the last My Hero Academia fans will see of the crafty villain.