Aetherhorn Unicorn

Whenever Aetherhorn Unicorn or another creature you control enters the battlefield, you get {e}. (One energy counter.)
Whenever Aetherhorn Unicorn becomes tapped, you get {e}.
Pay {e}{e}{e}: You gain hexproof until end of turn. Use this ability only as a sorcery unless you pay {e}{e} more.
Aetherhorn Unicorn's power and toughness is equal to the number of energy counters you have.