Terrier Patronus

Whenever enchanted creature attacks, put a
+1/+1 counter on enchanted creature. Then if it
has three or more +1/+1 counters on it, sacrifice Terrier Patronus.
When enchanted creature becomes the target of a
spell or ability your opponent controls, sacrifice Terrier Patronus.
Whenever you sacrifice this card, it deals damage
equal to this creatures power to any target.