Ceterinous, Hydra's Promise

Ceterinous enters the battlefield with X +1/+1 counters.
Whenever you cast a hydra spell, if that spell had
X in its mana cost you may add 2 to the X.
Whenever another hydra enters the battlefield
under your control choose one: Target hydra
gains haste until end of turn, Proliferate, Target
opponent loses life equal to twice the number
of hydras you control