I just had a game where I had a Robb Stark (KotS) in play with Shaggydog and Nymeria attachments, along with a Ghost (DotN). My Martell opponent attacked with three characters. Using Shaggydog's ability (Challenges: Kneel a Direwolf card to choose 1 attacking character. Until the end of the phase, that character gets -2 STR), I knelt both attachments and Ghost to reduce the strength of each attacker by 2. I then played At Night They Howl (Any Phase: Stand all Creature cards in play). I then re-knelt all three Direwolf cards to give each of the attackers another -2 STR, effectively reducing their total power to 0.

The question is - was that a legal play?

Sure, you can take as many Challenges: and Any Phase: actions as you want in the player action window after attackers are declared. The whole point of At Night They Howl standing your creature cards is so you can kneel them again for some positive effect : )

Nice! Glad we got it right. Thanks!