I'm hoping the inconsistencies with the background in Grinch Link are due to the printer / materials or whatever that were used. Due to the picture quality, some of the characters have parts that look like blobs, which is especially noticeable with Olimar's Pikmin, so it could even be that.
I also read that the photo of parts of the mural cut and put next to each other was actually someone taking them and then resizing / blowing them up, so that photo probably isn't even from the original person involved, especially since it seems to have been a Snapchat video that has somewhat-poor quality and had pictures taken from it anyway; but I dunno.
I personally believe that if this is fake, our alternative is Box Theory, and while Incineroar is cool and all (I mean, he could hit opponents with flaming chairs), I'd really like the characters in this leak. Vergeben also isn't the only one who claims Incineroar now, but so are a lot of the known insiders.