2/21/2013 - I've designed this card a few times. I'm amused by the idea that the cost to grow your creature increases with its size. The result is a card that's useful at any point in the game, that you can invest excess mana into, and that grows as you desire, but not in an unbounded fashion that requires it to be rare or mythic like Primordial Hydra.
I was tempted to make Direlion a one-drop with seriously wacky templating…
Put a +1/+1 counter on Direlion: Pay 1 for each +1/+1 counter on Direlion or sacrifice it.…but templating is not where you want to innovate. We need the already obtuse language of Magic to remain as consistent as possible.
As a bonus, I offer a mostly unrelated design using the same art. Yes, it's intentionally crazy good.
Eat your heart out, Lotus Cobra.
EDIT: Added the vastly superior version you all helped with: