Hydra, Sea Guard

{x} equals 18 you may sacrifice
creatures when you castit, If you
do this costs sacrificed creature/s converted
mana cost less to cast.
Hexproof, lifelink
This may attack up to 3 times per turn
When this attacks you may {10} and
this loses lifelink until end of turn if
you do return creature from any graveyard
to your control