He reminds me quite a bit of a summon in some kind of an RPG (but secret boss works too).
The conveniently placed crystals covering his lower body are beautifully drawn and I'm loving the way you shaded all of his muscles. The random lightning in the back also works wonderfully as a dramatic entrance. You did a lovely job drawing him and the coloring is gorgeous!
Goodness! Thank you for all your comments! They mean a lot to me Square Enix made Mario RPG and this secret boss was a tribute to their games. It even plays the Final Fantasy win music when you beat him