Egg-Freed Hydra

Whenever you cast a green creature spell,
put a +1/+1 counter on Egg-Freed Hydra.
{t}, Remove three +1/+1 counters from this creature: Mature Egg-Freed Hydra. Activate this ability only any time you could cast a sorcery.
(To mature Egg-Freed Hydra, exile it. If you do, search your library for a non-Young creature card
that shares a creature type with it. You may cast it
by paying the difference in mana costs between it
and this creature. Then shuffle your library.)