The Alphawolf is a badass wolf who once per game can give the wolves an extra kill.
The extra kill is subject to all of the same rules as a normal wolf kill. It can be blocked by a Protector. The Alphawolf can be killed by a Huntsman, and it won't work on a Vampire.
If the extra kill fails for whatever reason, the Alphawolf does NOT get another one, it's gone for the rest of the game!