Ordeal of Purphoros

Ordeal of Purphoros {1}{R}

Enchantment - Aura (CMC 2)
Enchant creature
Whenever enchanted creature attacks, put a +1/+1 counter on it. Then if it has three or more +1/+1 counters on it, sacrifice Ordeal of Purphoros.
When you sacrifice Ordeal of Purphoros, it deals 3 damage to any target.