Kuluuhn, Chaos Hydra

Kuluuhn, Chaos Hydra enters the battlefield with +1/+1 counters on it equal to the mana spent to cast it.
Each Hydra creature you control enters the battlefield with an additional +1/+1 counter on
it.
Hydra spells you cast cannot be countered.
{x}{x}{x} : Put X +1/+1 counters on each Hydra
you control.