This is a question of identity, and how these things interact:

Say Assassin's Strike has dealt damage after using its own E. Would it still be placed in the staging area if Possession Stance turned it face down? I ask because I am unsure if the clause "this attack" carries over to when the ability would finish. Because the attack would be face down, it would no longer be considered an attack (or possibly even "this attack") when the End Phase happens.

Really just a clarification, but one that is bound to show up.

Second thing. Can a multiple be turned face down again? Do they turn face up?

-Tinman

If a card in your card pool goes facedown, during the end phase it will be discarded unless another effect specifically acts upon said facedown card.

When the attack goes facedown, it will no longer be identifiable as the same card, so the effect will disappear.

So in this case, the original attack turned facedown by the action will be discarded during the end phase. The already facedown multiple copies that would otherwise have been discarded are moved to your staging area per the text of the Enhance.

We'll get back to you on the facedown facedown bit.

there was a conversation about flipping already facedown cards face down when siegfrieds new support had just come out. im fairly sure it ended up being that the face of a card never changes so itd be something akin to readying a ready foundation or commiting a commited foundation. the card is facedown and so there is no change being made.

someone was arguing that they should be able to turn facedown foundations face up if he had an effect that would turn them facedown again.

Yeah, that's my position on it... you can't flip a facedown card facedown because it's already facedown.

i'd say you could flip it face down again which is pointless. but if i say that then people might say they could commit a foundation twice

while it is a rules query, i see no reason to flip a multi copy since it is already face down, youre just wasting momentum. If you actually could flip a multiple copy face up while in your card pool, you would then be stuck with a card that does nothing, and is not ignored for progressive difficulty since its now face up, making it a bad choice anyway.

Stamps to those who said -" Facedown is facedown"

Stamp to Tag for the answer to the original question.