If Ygritte is used to steal (charagenda) Quentyn Martell (via Old Nan giving him the Night's Watch trait!) and then Valar is played, to whose House card does Quentyn go? We suspect it is the player who owns the Martell deck, as per the following note:

A Moribund card (and its attachments) is considered to have been killed, discarded, returned to its owner's hand or deck, or moved to its owner's shadows area, but only for the purposes of triggering responses and passive abilities. This includes responses and passive abilities triggered by a card being placed in the appropriate out-of-play area. A Moribund card is, for all other purposes, still considered in play.

However, we're not 100% sure...

You are correct, but it is a little more complicated than that.

Based on the note you found, Quentyn (or any character agenda) can only go to its owner's House card as an agenda. However, the text of a character is always read from the controller's point of view. So if an opponent with an agenda steals Quentyn, the "as your only agenda" part of his effect, read from the controller's point of view, will not be true, his effect will not activate and Quentyn will go to the (owner's) dead pile.

Long story short, if an opponent steals Quentyn and neither the opponent nor the owner have an agenda when Quentyn dies, he will become an agenda on his owner's house card. In all other situations, he will be put in his owner's dead pile.

Hi pal

I'm sorry, but I don't quite understand this yet.

If Quentyn Martell would be killed, instead attach Quentyn Martell to your House card as your only agenda.

There are two instances of "your" here. According to your post these both refer to the current controller of the card (Stark). As per the comment I found, for the purposes of triggering this passive ability, the card is considered to have gone to the controller's dead pile. So I can see two possibilites:

A) The card is considered to have gone to the controller's dead pile when determining the passive ability. Aren't they thus both the controller and owner of the card at that moment, meaning that Quentyn goes to the Martell agenda provided there is no agenda there already, regardless of whether Stark has an agenda?

B) On the other hand, if the controller has not changed, then the card will go to the dead pile of the Martell player whether or not the Stark player has an agenda? Because both "yours" mean the Stark player, but they can't have the agenda (presumably because the card can never go to the Stark dead pile?), so off it goes.

A very confusing situation for me!

There are a fair number of advanced timing rules involved with resolving this situation.

One of those advanced rules is that the text on these character agendas is not a passive ability that initiates once the card is put in the dead pile. It is a replacement effect that resolves when the character is being killed in the first place. So it starts off similar to what you have labeled "B" above: If the controller at the time of the character's death (Stark) has an agenda, the character is directed toward the controller's dead pile; but if they do not have an agenda, the character is directed to become the controller's agenda.

AFTER THAT, the comment you found in the FAQ (that a card must always go to its owner's out-of-play area) kicks in. If the character has been directed to the controller's (Stark) dead pile, it is placed in its owner's (Martell's) dead pile, and if it has been directed to become the controller's (Stark) agenda, it becomes the owner's (Martell's) agenda. BUT , is the Martell player already has an agenda, there is nothing in the rules or in the card text that allows the character to replace an existing agenda. So if the Martell player already has an agenda when the character would be placed there, the placement fails and the character goes to the dead pile -- the default placement for the effect that killed it.

Okay, thanks very much for your patience pal, I think I understand now!