Creature — Spirit Wolf 4/2, 5G (6)
Uncommon
Creatures with power less than Howlgeist's power can't block it.
Undying (When this creature dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)
Illus. David Rapoza

5/1/2012: The comparison of power is performed only when blockers are declared. Increasing the power of a blocking creature (or decreasing the power of Howlgeist) after this point won't cause any creature to stop blocking or become unblocked.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Extended (Type 1.X)
Legal in Standard (Type 2)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern