I have no idea if someone might have already done it or not, but I think a story similar to A Mew Adventure by JorieDS which I totally hope posts more chapters I love the author's story. A person reincarnates as a mew in the anime world of MHA maybe with a human form maybe not upto the person who writes the story so yeah a mew with the moves and forms of all the pokemon available currently including the legendaries and mythic or that might be to op eh the mc can either not have them or he works his way upto them as I say upto whoever chooses to write this story.