Creature — Hydra 0/0, XGG (2)
Mythic Rare
Primordial Hydra enters the battlefield with X +1/+1 counters on it.
At the beginning of your upkeep, double the number of +1/+1 counters on Primordial Hydra.
Primordial Hydra has trample as long as it has ten or more +1/+1 counters on it.
Illus. Aleksi Briclot

9/22/2011: Consider only the number of +1/+1 counters on Primordial Hydra when determining if it has trample, not its power and toughness. For example, a Primordial Hydra with six +1/+1 counters on it that's been the target of Titanic Growth (giving it +4/+4) would not have trample.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Extended (Type 1.X)
Legal in Standard (Type 2)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern