The following contains major spoilers for My Hero Academia Chapter 362, "Light Fades to Rain" by Horikoshi Kohei, Caleb Cook and John Hunt, available now in English from Viz Media.
My Hero Academia’s Shigaraki Tomura has had one of the most dramatic ascents to power in all of anime. From being entirely dependent on disposable henchmen to taking on Japan’s greatest heroes solo, Shigaraki has had more growth than villains typically enjoy over the course of their story arcs -- and apparently he wants everyone to realize that. After yet another pointless attack by the heroes in Chapter 362, Shigaraki spelled out just how powerful he’s truly become.
In a bid to protect all present on UA's grounds from Shigaraki's advance, the Big 3 prepared their most dangerous combo attack: Amajiki's ultimate Vast Hybrid form amped up by ingesting a portion of Nejire Hado's energy. The blast would've been a fatal hit against any other enemy, as it was powerful enough to break through the electromagnetic barrier surrounding UA. However, Shigaraki's invulnerable body allowed him to easily shrug off most of its impact.
Amajiki's Vast Hybrid Plasma Cannon completely disintegrated the extra limbs Shigaraki had created with Simple Growth, but was ineffective against his main body. In fact, the heroes' continuous guerrilla warfare must've enraged him, because he suddenly began to disparage the attacks directed at him so far. Shigaraki insisted the heroes still didn't understand his true power, and that their ignorance was why they still thought he wasn't going to win that fight.
Shigaraki went on to describe Amajiki's Plasma Cannon as pathetic and asked all the heroes present if they thought it would have been effective against All Might when the Symbol of Peace was at his prime. Admittedly, as impressive as Suneater's attack was, it would have been equally redundant against All Might. Ironically, Shigaraki's prideful boast was finally beginning to give the heroes an idea of the Herculean task ahead of them.
For all intents and purposes, Shigaraki is All Might -- albeit an alternate version of the Symbol of Peace that one day developed a soft spot for villains. While All Might's unrivaled power allowed him to usher in an era of peace that no villain could threaten, now Shigaraki is attempting to create an era of complete villain domination. He's already self-described as the Symbol of Fear and has been vocal about his anti-hero sentiment ever since he was introduced in My Hero Academia. Now that he has the power to make real change, he's attempting to reshape the world in his own image.
The most terrifying aspect of Shigaraki's strength is that all his exploits so far have been accomplished while he's only had access to a fraction of his power. Since he stepped on UA's grounds, Shigaraki has been under the effect of the Erasure Quirk, preventing him from using the true gifts of the All For One Quirk. The power he stands to unlock once he regains access to his Quirks is inconceivable. It's hard to imagine how even Deku will deal with a villain who has All For One's Quirks and All Might's raw strength.