Yritaxetl, Forests' Mystery

Yritaxetl, Forests' Mystery enters the battlefield
tapped with ten -1/-1 counters on him.
Whenever you draw one or more cards, you may
have Yritaxetl become a green and blue Nephilim
creature with hexproof and trample until end of
turn.
{1}, Remove a +1/+1 counter from a creature you
control: Remove a -1/-1 counter from Yritaxetl.
Activate this ability only any time you could cast
a sorcery.