Patron of The Hydra

Hydra Offering (You may cast this card any time
you could cast an instant by sacrificing a Hydra and
paying the difference in mana costs between this and
the sacrificed Hydra. Mana cost includes color.)
Patron of The Hydra enters the battlefield with
X +1/+1 counters on it.
Whenever you cast a Hydra creature spell with a
mana cost that contains {x}, double the value of
X.