Things I believe point towards the leaks being fake on the front page:
Betternet Leak:
1) New Pokemon Trainer (telling you right now it isn't going to happen)
2) Lots of obvious points (release date at E3, Little Mac, etc...)
3) At this point in development, I don't think people can say cuts have been made yet. Sakurai isn't planning on going cut crazy, so cutting 4 characters is quite a bit
Calling this fake
Jumpman Leak:
1) Jumpman IS Mario
2) Roster will likely be over 40 characters. For it to be 40 at this point, there would need to be 4 cuts made.
3) Makes plenty of generally easy predictions on Assist Trophies
I think this is fake as well
Can't prove they're fake, and I have feelings similar to this on all but the Palutena Leak. They all just seem...too generalized or too fan specific. Hard to explain.