Playable on a face-up Agent who can use shadow-magic. If agent is revealed and not in a Free-hold [F] or Haven [H], he can tap to allow any Undead hazard creatures to be played at his site this turn. Any Undead hazard creature so played do not count against the hazard limit.
"A shadow came out of dark places far away... Barrow-wights walked in the hollow places with a clink of rings on cold fingers, and gold chains in the wind."
-LotRI