Shigaraki is a twisted and evil man, not only did his quirk, Decay, that makes it to where anything he touches with his five fingers instantly start decaying, losing the effect after he removes his fingers from the area, but he also has All For One, a quirk that lets him take other people’s quirks, meaning he has a lot of powers, he thinks of being a villain as a video game, where the heroes he fights are different level enemies and bosses, All Might was the final boss, so to speak.