First up is Gilgamesh from fate zero. While he can be defeated it takes a crap ton of work. Firstly you have to get past all the swords and weapons that come out of the gate of Babylon, but you also have to do it before he uses his final sword which can destroy all of creation. Also he can teleport.
Next is Tatsumi from Irregular at magic school. He appears to just be a normal guy but he has the magic sequence of restoration memorized so he pretty much can't die. Also he can separate molecules with a karate chop and shot a blast from a rifle that is equivalent to a hydrogen bomb probably even stronger than it.
Thirdly is Sosuke Aizen. Where do i even start with this one. First before his transformation he was said to be at least twice as powerful as your average captain level soul reaper. Also he took down most of th captains with his own skills. Also his zanpakuto allowed him to completely hypnotize anyone. After he transforms he was near invincible and even after the final getsuga tenshou he was only sealed away.p
Lastly is a oldie but a goodie Mr.Bison. He was pretty much invincible and it took both Ken and Ryu to take him down. His fighting skills combined with is psycho power makes him pretty much superhuman considering he was shot three time and his psycho power just heal him and block aby other bullet.