Masahiro Sakurai, the creator of Super Smash Bros., just posted this image to the game's Miiverse feed; it was then published to its official page. Those antlers belong to Xerneas, The 16-point Pokébuck who debuted in Pokémon X (and on its cover) last week, so look for him to appear in the game in some form.
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Did anyone else after catching the version legendary just immediately cram it into the PC? I didnt really care to use Yveltal on my playthrough.