Something occured while me and two friends were playing the other day, that i would like to get a clear answer on.
I was playing Stark, player to my left was playing Martell, and player to my right Greyjoy. There were several cards in play, but the important cards for this question is my (stark) Greatjon Umber (core: Challenges: Kneel Greatjon Umber to have him participate in the current Military or Power challenge as either the attacker or as the defender.), and Greyjoy's Scouting Vessel (Challenges: Kneel Scouting Vessel to choose a defending character. For the duration of the challenge, that character does not count its STR.)
Martell is first player, and once we get to challenges phase he passes. Greyjoy is now the active player. He initiates a power challenge against Martell, and kneels a character. Everyone passes player actions. Greyjoy chooses a character to stealth, and in doing this Martell can't defend the challenge.
Another player action window now opens. Martell passes, Greyjoy passes, and i activate Greyjoy Umbers ability to defend for the Martell player. Greyjoy now wishes to activate Scouting Vessel, since there now is a defending character to use it on.
My question is: can he do this, considering he already passed his turn to take any player action?