Harry Potter: The Legendary Wizard Starts with Avada Kedavra

[Invincible + Slytherin] (with some imagined worldbuilding)

Xu Wang transmigrates to the Harry Potter world and becomes Micale Osavage, the young master of the Osavage family. The fallen family has only an old butler left, but he unexpectedly obtains the Legendary Wizard System. From the start, he is proficient in the fundamentals of magic and receives a max-level Avada spell. He also discovers in secret that his family seems to have an unusual connection to time.

And so he is granted infinite magic and the talent of a potion genius.

Dumbledore: "He is the heir of time, an absolute genius. I hope his appearance will be a good thing for the Wizarding World."

Voldemort: "Damn it, why is it him every time? Will the nightmare of time engulf the Death Eaters!!!"