This could be either some form of the others attacking, natural disaster, or most likely to a smaller degree (maybe changing the tide in a battle between northman and the freys) the riverland wolf pack. We know they have some significance as they've been talked about a ton but nothing has happened with them. Plus, Nymperia def knows the frey's killed her brother. And it's fitting that the old gods or some vessel of the old gods aka the STARK wolfes give retribution to the frey's for breaking their age old law of guest right.
Edited by drayrock, 20 February 2013 - 05:25 PM.