The following post contains spoilers from chapter 274 of My Hero Academia. You have been warned.
We finally got to see a true taste of Tomura Shigaraki’s new powers as he fought Endeavor. It looks like Shigaraki really has become an overpowered monster despite being only 75% complete. Let’s have a little overview of what Shigaraki can do so far. His Decay quirk can disintegrate entire cities. He not only gained the All For One quirk, but he also inherited every quirk All For One accumulated over the past several decades. Among those quirks are regeneration, which is demonstrated when Shigaraki could heal his body faster than Endeavor’s flames could damage it. Then Shigaraki demonstrated either an energy blast or air pressure cannon like the one All For One used against All Might. He was able to catch Endeavor off guard with this quirk and firing it point blank range in Endeavor’s face. It is then revealed the All For One the person never had Ragdoll’s Search quirk. While All For One did indeed steal Ragdoll’s quirk, he entrusted it to Doctor Ujiko to give to Shigaraki when the time was right. Shigaraki used the Search quirk to locate and target Izuku Midoriya. Then Shigaraki either flew at supersonic speed like Superman or jumped really high like the Hulk while he was pursuing Izuku. Shigaraki could even fend off Endeavor’s flames with his bare hands.
What was even more frightening about Shigaraki’s upgrade was the fact that he was not putting any real effort in his fight with Endeavor. If Shigaraki did put any effort, Endeavor would be dead right now. Instead of fighting seriously, Shigaraki was distracted by a sense of emptiness that was plaguing his mind. A voice in Shigaraki’s mind was compelling him to get his hands on One For All. It looks like in addition to inheriting the All For One quirk and all the powers that came with it, Shigaraki also inherited the side effects that came with it. Because of its nature to steal and accumulate quirks, the All For One quirk seems to give its user an insatiable desire to steal quirks that interest them. All For One himself stated that stealing quirks he likes is a bad habit of his, but I think it was something more than just a bad habit. Now that Shigaraki has inherited this side effect and has a fascination with One For All, he will be relentless in hunting Izuku down to the ends of the Earth. To make matters worse, now that Shigaraki has the Search quirk, there is nowhere for Izuku to hide. Shigaraki has proven able to fight someone as strong as Gigantomachia for one and a half months while Izuku does not have that level of endurance yet. That means that Shigaraki will run Izuku ragged until he is physically and spiritually broken while Shigaraki himself remains strong.
When Izuku started displaying the quirks of the previous wielders of One For All, fans thought Izuku was becoming too overpowered. Now, we know why Izuku was becoming overpowered. Because he was being set up to battle an even more overpowered supervillain. So far, we haven’t truly seen what Shigaraki is truly capable of because he was holding way back. In future chapters as Shigaraki confronts Izuku, he may start taking the fight seriously and really put his back into it as he tries to take One For All from Izuku.