Looks like I missed a lot last night. To think there's a new leak where one of the keys to busting it is the damn Grinch who stole Christmas. What a world.
As for the leak itself, I'm not sold on it. Although it'd be incredibly difficult to recreate the banner, cutting out every character and moving them one-by-one, all while having to fill in the blanks from the background. Yet it isn't impossible, and the image being small and blurred is convenient for hiding errors/inconsistencies with the art.
Plus, the roster size her seems way too generous. Ten newcomers and six clones is a pretty big amount, and seems even more unlikely when you factor in the seven returning veterans. That's a net increase of 23 fighters over Smash 4. As for the possibly leaked characters themselves, they all have their merits, and no-one sticks out too badly. Mach Rider could actually be pretty cool, the more I think about it.
Lastly, I don't think the lack of a new Pokemon itself busts the leak. With essentially three returning Pokemon characters, Sakurai may have felt that adding a new Pokemon wasn't as much of a priority. I know Sakurai has stated he sets aside a spot for a new Pokemon and a new Fire Emblem lord, but the latter doesn't seem to have taken place, as Chrom is an older character and just a clone. Still possible we can see a new Pokemon as DLC, though.