This is fake. Look at below of the Pokemon, it looks like it has graphics from SM.
Look at this:
https://imgur.com/a/tADenQg This image is blurry. Most if not all fake leaks are blurry. Oh and the wings... Look off.
Next, look at this:
https://imgur.com/a/4NSii1b Oh god the eyes, why are these so big?! They look so ugly
https://imgur.com/a/N0ToLlf The borders looks a bit broken, if not weird.
https://pbs.twimg.com/media/EIVreXoWwAIV-VJ.jpg This doesn't look like the Grimmsnarl. Something about his head looks off. And he's supposed to look like a smelly, ugly person..
https://imgur.com/a/Sj0aRxA This is ugly, also there are some cyan colours.. Isn't the theme purple?
https://pbs.twimg.com/media/EIVnVl6WsAAVN9s.jpg This looks like it was made for a mobile game
Point is, most of the leaks that could be real are mixed in with fake leaks. You should already be disproving them.
