All For One is the greatest evil in the world of My Hero Academia and, at the same time, one of the most intriguing characters in the story. Known as the demon lord himself, All For One is responsible for the vast majority of crime in Japan.
He's incredibly powerful and with his Quirk, he has shaped the world of My Hero Academia and played a major role in the overarching plot of the series. All For One has lived for over a century and, that is precisely why he is as big a threat as he is today. Over this period of time, he has gone through several transformations, with each one of them being stronger or weaker when compared to the others.
5 All For One Post Kamino
By far, the weakest form of All For One that fans have seen is the one after the events of Kamino. In Kamino, All For One fought against All Might for the second time, and, even though he had a tremendous number of Quirks at his disposal, he ended up losing this fight when All Might used every last spark of One For All left within him and took him down.
All For One was, subsequently, locked away in Tartarus and it took him quite a while to break free from there. Once he had broken free, he no longer held the real All For One quirk and, as a result of the fight that he took part in, he was severely weakened. His plan was to raise Tomura and take control of his body later on and that in itself is an indication that he knew that his body was not strong enough anymore. This form of All For One is certainly the weakest that the fans have seen in the story so far.
4 All For One After The First Fight With All Might
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All For One fought All Might a bunch of times throughout his life and their first clash came before the story even began. At this point, All For One was likely closer to his prime and stronger than fans know him to be in the first part of My Hero Academia. Despite being stronger and having much better control over his All For One Quirk, he ended up falling to All Might all the same.
This is because All Might was in his prime at this point in time and was stronger than he was in Kamino. All Might defeated All For One, however, he didn't come out of this battle scratchless. All For One delivered a telling blow to him, ruining his internal organs in the process. This injury became the reason for All Might's downfall and he ended up looking for a successor because he knew he couldn't remain the Symbol of Peace for too long.
3 All For One In Final War Arc
In the Final War arc of My Hero Academia, All For One revealed an entirely different level of strength when he fought against Endeavor and Hawks. He pushed them to their absolute limits and showed different Quirk combinations that the fans had not seen before. His preparations leading to this war were proof enough that he was actually stronger than when he fought All Might in Kamino.
Undoubtedly, All For One was on a different level entirely in this fight and he even managed to take on multiple Heroes at the same time. Despite his great level of strength, he fell to Endeavor and resorted to his trump card, which he ended up revealing later on.
2 Prime All For One
Back in his prime, All For One was at the pinnacle of his abilities. Fans have not yet seen much of prime All For One, however, what they do know is the fact that he killed several vestiges of the One For All. His powers were such that none were able to compete against him. Even the mightiest of heroes eventually fell to him until he ran into Yagi Toshinori, famously known as All Might.
In his prime, All For One had much better control over his Quirk. He is known to have had the powers to store more Quirks within himself as well as use more combinations at the same time. On top of this, his body was also much faster, stronger, and more durable than it was later on. All these boosts mean that Prime All For One was a different beast altogether and the only one capable of matching him in battle was none other than the Symbol of Peace, All Might.
1 Beyond Prime All For One
In the Final War arc of My Hero Academia, All For One has shocked the fans by surpassing all of his limits. After using the rewind drug, his body keeps on rewinding and he reached his prime state, which wasn't all that much of a surprise to the fans. However, the rewind drug did not stop there. In fact, his body kept rewinding to an even more youthful state. It is evident that All For One has actually surpassed his prime by making his body even younger. He is now much faster and stronger than he ever was before.
His control over the All For One Quirk has reached an unprecedented level and he can store as well as steal many more quirks at the same time. The combinations that he is using are strong enough to destroy cities within a matter of seconds. He can take on the entirety of the Hero Association all by himself and he has lived up to his name as the greatest villain of all time. The only downside of this transformation is that it is temporary and he will eventually revert into nothingness. That said, All For One is, undoubtedly, beyond his prime right now and this is his strongest form ever.