Spellgorger Hydra

Whenever an opponent casts a spell with a converted mana cost higher than Spellgorger Hydra's power, put X +1/+1 counters on Spellgorger Hydra where X is the difference between that spell's converted mana cost and Spellgorger Hydra's power.
As long as Spellgorger Hydra has 7 or more power, it has trample and hexproof.