Let’s say right around the time of All Might’s retirement fight with All for One, Mewtwo (First movie & MR version) teleports into the world.
Mewtwo gets his fancy cloning lab on his island (positioned about 20 miles off the coast of Japan) and his goal is largely the same as the first movie; demonstrate his superiority to humans and then exterminate them.
How does the ‘verse change? Does a massively powerful telekinetic with mind control abilities and advanced cloning facilities upend the balance of power in the world?
EDIT: Feel free to discuss other time periods in MHA as well if they’d be more interesting. Say late season 4. (I’m not up on the manga, but don’t let that stop you, though spoiler tags would be appreciated for stuff not yet animated).