Full Cowl at 100% dramatically increases all of Izuku's abilities, granting him strength and speed that rival that of All Might, and the ability to move through mid-air using wind pressure. At 100%, Izuku completely outmatched Overhaul in his final form.
Most importantly, Deku can use the OFA Quirk at 120% of its original power, surpassing All Might himself. For the sake of comparison, 100% was enough to effortlessly defeat Overhaul back in the Shie Haissaikai arc, and he's one of the strongest villains in the series.
As he gets more experience and works out, he gets stronger. Pretty simple. In this analogy, at 100% both Midoriya and All Might are at the same footing, with the same stats and everything. HOWEVER, Midoriya has a special ability: He can change his stats and All Might cannot.
That means he can carry objects 3.5 times his body weight.
While Deku can only use around 25% of his One for All powers in the anime, and while on the last given account he was able to use 45% without damaging his body, it is implied that he has a way of unlocking all 100% of it using a combination with his other abilities such as Fa Jin which he acquired from the third holder ...
Even his 100% punch isn't enough against the guy. Then in a last minute effort after the water boy distracts the muscle guy with his power, Deku turns his power up to a million percent.
The power of Rimuru is immense, only topped by the likes of Milim the demon lord. Rimuru is not just stronger than Deku, but even Endeavor, My Hero Academia's current Number 1 Hero, would lose to him.
Midoriya, in the manga is able to use 8% of One for All without experiencing any pain. However, when push comes to shove, he is able to maintain the continuous flow of 20% One for All in his body for a short period of time..
Deku's final quirk is known as 'gearshift'. It's a quirk that is activated via physical contact. It allows the user to change the velocity of anything they touch, meaning they can spontaneously slow things down, or speed things up.
Overdrive is an exceptionally powerful ability in the arsenal of Izuku Midoriya. It might even be the strongest power that he has up his sleeve right now. Overdrive activates when Deku uses transmission with Fa Jin.
In the My Hero Academia universe, children often inherit one of their parents' abilities or powers from a combination of both. According to Deku's mother, the inherited quirk Deku should've naturally received would've either been his father's quirk, breathing fire, or her own ability to levitate small objects.
All Might is certainly the strongest character in MHA so far. Born Quirkless just like Izuku, All Might received the power of One For All from his mentor, Nana Shimura.
The fact that Endeavor's self-doubting conscience therefore tries to tear him down by saying that he'll never be like All Might, but Deku proves that Endeavor believes that Deku has already succeeded All Might.
As of now, Deku has access to seven Quirks, namely One For All, Transmission, Fa Jin, Danger Sense, Blackwhip, Smokescreen, and Float. The basic gist of all these powers is that they all come from the previous One For All users, with their abilities becoming stronger throughout the generations.
Deku Goes 100% In My Hero Academia Episode 76 'Infinite 100%' — The Boba Culture.
My Hero Academia: Deku's Final Quirk Makes Him Faster Than Prime All Might. Deku reveals the second One For All user's Quirk in Chapter 368, making him faster than the legendary hero All Might.
After reading a few official theories about Deku having a quirk before, many canon claims said that the Doctor himself was the person who STOLE Deku's original quirk, which could've been Fire Breath or something like that.
After observing how the quirk reacted to the bodies of the users, all the previous wielders concluded that One For All could not be held by a user who already had a quirk. Thus, Deku is the last successor to the quirk, making him their last hope to take All For One down.
According to the events of My Hero Academia so far, Deku grew up without a Quirk. He was given the OFA Quirk when he met All Might. The series does give an explanation for why Deku was deemed Quirkless.
His overall limit increased to 8% after inventing One For All: Full Cowl - Shoot Style and fighting with Katsuki. Izuku can freely adjust the percentage of One For All at any time, but going over his limit will cause damage to his body.
Anime Debut
The Luminescent Baby (発光する赤児, Hakkō suru akago?) was the first person in the world born with a Quirk.
All For One is incapable of stealing One For All from its wielder, as that Quirk, by its very nature, can only be passed on if the present wielder wills it. Thus, wielders of One For All can act as a natural counter of sorts against All For One's ability to steal other Quirks.
It's impossible to ignore, considering his potential, when talking about strength. Moreover, Deku's quirk, "One For All", inherited from All Might himself, naturally secures his spot as the strongest in his class.
Izuku is the last user of the One For All and also the one who goes on to become the strongest. Izuku was given this power by All Might when he was looking for a successor following the aftermath of his fight against All For One.