The 3D portraits on the character select screen are based on character artwork from some of their home games. Mario's render is from Super Mario 64; Link's is from his artwork for The Legend of Zelda: Ocarina of Time; Donkey Kong's Donkey Kong Country artwork is the basis for his Smash portrait; Yoshi's comes from Japanese artwork for Yoshi's Island; Kirby's is from Kirby's Adventure artwork; Fox's is taken from Star Fox 64; Captain Falcon has a 3D realization of artwork from F-Zero X; Pikachu and Jigglypuff are 3D versions of Pokemon Red & Blue concept art; Samus Aran's comes from Super Metroid; Ness's is a redone done version of his Earthbound art; And Luigi's appears to be taken from Mario Kart 64.
Contributed by PirateGoofy