What do you guys think? Is First Snow enough to push you into running this Arya vs Core? 

I still just don't think she cuts it (especially when you consider that Core Arya comes into play duped). 

I mean, targeted kill is nice, don't get me wrong, but discarding a 4-cost character (in Stark) to get rid of a 3-cost character across the board is asking a lot--especially as you've just lost a character anyway. And this effect isn't even immune to Save effects. 

And that's not even taking into account Septa Mordane is obviously geared towards Core Arya. 

In melee, can you pick a character from a non attacking opponent to kill? 

For example, player A attacks me and triggers Arya's ability, Can I kill one of character B's characters, like Margery Tyrell?

I don't see why you couldn't, unless there is something in the basic rules of the game preventing that, but we're kind of new and have missed rules before. 

Question: Arya is in play and she is one of 5 stark characters in play under the control of one player. Wildfire is played. She is not chosen as one of the cards to live so she dies with one other stark character. Can her ability still trigger? or can it not since she is one of the characters chosen to die?

Question: Arya is in play and she is one of 5 stark characters in play under the control of one player. Wildfire is played. She is not chosen as one of the cards to live so she dies with one other stark character. Can her ability still trigger? or can it not since she is one of the characters chosen to die?

At a guess, I would say no, since all characters from Wildfire die simultaneously (including Arya); therefore - when she is on the board and her reaction is "looking" for a dead Stark target, there are none. Once Wildfire has completed, all characters die (including Arya), so she is not able to be sacrificed for her effect.
Death from wildfire is a "must do," Sacrifice to pay for an effect is a "may do."

Now, if you chose Arya to live, then 2 characters die from wildfire, her reaction triggers, and now you may sac her to kill an additional opponent's character.

I'm not a dev/ rules guy however, but that is how I would read it.

Bring back moribund!

It's simple really, it's the difference between Interrupts and Reactions.

Wildfire resolves:

1. You choose the characters that are [not] going to be killed.

2. Their death becomes imminent. You can trigger any Interrupts to them being killed.

3. All characters not chosen are killed, simultaneously.

4. Reactions to them being killed can be played. At this point Arya is in the dead pile, not in play.

5. All players who say "moribund" are removed from the game.

Bring back moribund!

Even under the moribund rule, she wouldn't have been able to trigger her reaction if she was the Stark character killed. You can't sacrifice a character that is already moribund:dead.

It's simple really, it's the difference between Interrupts and Reactions.

 

Wildfire resolves:

1. You choose the characters that are [not] going to be killed.

2. Their death becomes imminent. You can trigger any Interrupts to them being killed.

3. All characters not chosen are killed, simultaneously.

4. Reactions to them being killed can be played. At this point Arya is in the dead pile, not in play.

5. All players who say "moribund" are removed from the game.

so if Valar hits and Jory is in play (with no dupes), you can trigger jory to save Eddard for instance because his text is an "Interrupt" instead of a "reaction"?

He isn't actually referring to the moribund rule, he's using it as a way to say "good old days". It's a current trend

so if Valar hits and Jory is in play (with no dupes), you can trigger jory to save Eddard for instance because his text is an "Interrupt" instead of a "reaction"?

yeah you can even use him to soak a 2 claim mil claim all by himself and he wont even die. by choosing lets say Eddard and Jory for claim you can then sac Jory to save Eddard and nobody dies