Notes:

Since I posted the original set of proof, I figured I should post this as well. Basically, another version of the empty Battlefield that the characters stand on in the banner was found among E3 promotional footage, and when comparing this version of the stage to the empty one in the leak, they differ at various points where characters would normally obscure the background. The biggest change by far is the leaked version entirely lacks a castle seen in the background behind where Bowser would be. Look at both sides of the first "dividing line" in the leaked version, then compare that general area to the E3 version.