Whenever Pyreheart Wolf attacks, creatures you control gain menace until end of turn. (They can't be blocked except by two or more creatures.)
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.)
1/22/2011 Pyreheart Wolf's first triggered ability also affects creatures that weren't on the battlefield when it resolved but enter the battlefield later that turn. While this normally will have little impact, it could matter if those creatures enter the battlefield attacking or if there are multiple combat phases that turn.