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 (This creature can deal excess combat damage to the player or planeswalker it's attacking.) as long as it has ten or more +1/+1 counters on it.