This is Vulcan's Mega Charizard Y appearance.

Just as a bit of a backstory for those of you just tuning in, Vulcan through means of having his wish granted by Jirachi, was given the ability to "Mega Evolve" without the need of human intervention, however it is purely cosmetic as Vulcan obtain's no 'stat boosts' for becoming either Mega Charizard X or Y.

The only advantage Mega Evolving grants him is the ability to change his ability from Solar Power (as a regular Charizard) to Tough Claws as X or Drought as Y

It is very rare regardless to see Vulcan take this form, as he has a very high preference for being X over Y (though of course some alternate universe Vulcan would probably prefer Y over X)