Urakul, Aether Obliterator

Urakul can't be countered and has hexproof.
When Urakul enters the battlefield, you gain
10 life and draw 10 cards, then add {10} to
your mana pool. You have no maximum hand
size for the rest of the game.
Urakul's power/toughness are equal to the
number of cards in your hand plus X.
Flying, trample, vigilance, annihilator 4