The three rumored pokemon were supposedly leaked earlier yesterday. And I thought spriting with each release had been done for Gen. VI! At least, I wasn't prepared for leaks like this. Now smealum says there are unveiled mega-evolutions, too!
I've now updated the sprites with backs (Thanks, smealum!), and I made Volcanion almost 20% bigger (from about 80 to 96 pixels). The sprite is a tad too big now, although it now sizes nicely with Gigalith and Heatran instead of being dwarfed by them. I don't know what Hoopa's back looks like, so I made something plausible. I sorta know what Volcanion's back looks like, except I don't know the colors, so I guessed.
These designs likely belong to Game Freak; I do not own them.