In My Hero Academia, almost 80% of the population possesses a Quirk, a special ability that gives its user any type of superhuman power. Among them, we have All for One, the villain of the story, who poses the greatest threat to peace and tries his best to overthrow the Symbol of Peace, All Might. As he orchestrated his plans remaining low profile, viewers often question just how powerful is All For One in My Hero Academia?
All for One’s power is hinted at in his name itself. His ability allows him to steal other people's quirks and wield them as his own. Additionally, he can also use this stolen quirk and distribute it to others. It effectively makes him overpowered as a one-man army and a creator of his superpowered followers.
He was one of the first known individuals to develop a quirk, and his unique ability to steal others' powers instantly gave him an advantage. All for One exploited the fears of the vulnerable people who were figuring out this new power they seemed to have inherited.
This caused fear and confusion in their hearts. Disguised as a savior, All for One offered the troubled people to take away "cursed" quirks and then granted the stolen powers to his loyal followers in My Hero Academia.

Using his charisma and power, it did not take long for him to rule the underworld and become a tyrannical overlord. All for One decided to rule from the shadows, and as the story continued, he remained a looming threat for generations. He also fought against his brother, who has the power of One For All, a quirk of his brother that allowed him to pass his powers to another person.
Although his brother eventually passed away, the power of One For All lived on, passed from one user to the next, each training to one day defeat All For One. This Quirk was also seen as the Symbol of Hope, and as it was passed to the next user, it grew stronger. Finally, it reached Toshinori Yagi, better known as All Might, the seventh holder of the power. He was truly the first one to pose a challenge to All for One in My Hero Academia.
Even after he was heavily injured by All Might, All for One did not give up. From working in the shadows, he created the League of Villains and recruited people whom he believed would serve his ultimate goal: destabilizing society and creating chaos.
He particularly mentored Tomura Shigaraki, who had a dangerous quirk known as Decay. He was also chosen to not only serve him but also become the ultimate vessel for All for One.
Throughout the story, All for One collects many superpowers. Some of them include him stacked with strength-enhancing quirks, as they are pretty useful to overpower the most physically powerful heroes.
Furthermore, he also has his signature attack, Air Canon, which is used to produce massive shockwaves that can even destroy massive buildings with ease. Another quirk he relies on is Warping, which can be used for teleportation. Throughout the story in My Hero Academia, he steals over 30 quirks from others.

To understand his powers, let us look into one of the most iconic battles in the series, All of One versus All Might, during the Kamino Ward incident. At this point, All for One has already been heavily injured by All Might from their previous fights, yet he managed to unleash his numerous quirks.
Even in his weakened form, he managed to burn through the last embers of One For All from All Might. In front of the entire nation, All for One almost managed to shatter the Symbol of Peace. Although he was captured and imprisoned in Tartarus, his plans did not stop.
During the Final War arc in My Hero Academia, All For One took full control of Shigaraki’s body by fusing his consciousness with it. Meanwhile, he also managed to escape from Tartarus and used the power of stolen quirks to restore his body.
With both his original body and Tomura Shigaraki under his influence, All For One launched a final all-out attack on Hero society. He fought against Endeavor and Hawks and manipulated the battlefield with ease. It was at this time that he had finally unleashed his true potential and was the ultimate threat not only to the Hero society but also the whole world in My Hero Academia.
The Fall of All For One in My Hero Academia

Despite decades of manipulation, chaos, and unmatched power, All For One's time in My Hero Academia finally came to an end. As the final war came to its conclusion, the very vessel he had groomed to take over Tomura Shigaraki began to reject him. Finally, he was stripped of control and weakened. Therefore, unable to maintain his physical form, his quirk began to backfire. It is shown that his body regressed to a childlike state, and his consciousness started to fade, and soon he was reduced to nothing.
In conclusion, All for One was one of the most powerful characters in My Hero Academia. From his birth, it was as if it was decided that he was selfish and would continue walking down the path of darkness. His reign lasted for generations, with no one who came close to defeating him. Furthermore, he wasn’t just powerful, but he was also intellectually capable of making elaborate schemes that would support him. If All Might had not significantly weakened him and Tomura Shigaraki had not rejected him, it would have been next to impossible to defeat him.