I didn't see anything about this in the 2nd post, so here goes:
Argument: Assuming the leak is fake, the leaker obviously had to take care to make the profiles on the CSS match the ones that we saw already in the E3 demo. Now, there are also a ton of characters who weren't in the demo, so for those characters' portraits, it's okay to just make them up, right? Well, it turns out we HAVE seen the character portraits for a bunch of characters that weren't in the demo, seen at :46 here in the 3DS trailer:
and if you look closely at that part of the video and the CSS in the leak,
the cropping in many of the portraits, notably all of the characters who weren't in the demo, are different.
(Many of the differences might be hard to spot for some, but basically they are cropped differently. For instance, in Peach's portrait in the trailer, her crown is cropped out, whereas in the one in the leaked CSS, it isn't)
The counterarguments here could be:
A. They changed the cropping of the portraits since the demo (why?)
B. The team portraits aren't the same as the ones used in the 3DS version's CSS (However, a lot of them are)
C. The leaker doesn't overlook things. see: CPU bold line thing (Well, I agree the leaker has a meticulous eye if these are fake, but it is possible they overlooked this one thing)
This certainly isn't hard proof of anything, though I think it reduces the leak's believability just slightly.
(Credit goes to my friend Sarah for helping point this out)