At the start of a turn, let’s say the Mask is in the Matriarch’s trash. Matriarch plays Darken the Skies. The Mask comes back. Does it go off immediately? Meaning, since a non-fowl card was played (Darken the Skies, or even the Mask itself), she will play the top card of the Villain deck.
I’ve always played that it does. Am I making things too hard on myself? I couldn’t find any clarification here.
I’ve always played that it does NOT trigger. The reason being, the mask triggers off the playing a non-fowl card, and Darken the Skies has already been “played” (and is resolving) in order to bring the mask back. I make no claim that this is an official ruling, it’s just how we’ve played it.
I came here to back the interpretation that the next villan card would be played. However, after reading through the thread and some careful deliberations, I am (slightly) inclined to agree with broccoli.
Presumeably a card enters play before its text is applicable. Therefore the time for the effects of the mask would already be passed once the mask enters play.
Agreed, DtS is already processing its effects thus it is already in play and cannot “enters play” again, and that’s the key phrase on the Mask.
Edit: Huh, never noticed it before but it’s “each turn” meaning playing with the Pillars of Hercules in play (or a similar environment) where the top card of the villain deck is played every turn could cause the matriarch to flip many times during a single round, scary thought.
Agreed! And we have so many sentinels points between us that you all should each carefully decide for yourself rather than taking our opinions as meaning anything in particular.
Like I said, I had always gone ahead and kept playing cards, like awp - I learned from him. But that choice in wording is what brought me here.
There was no point to killing the Mask before - it would just come back right away and keep on chugging. That also eventually tipped me off that something may be off. 
Anyway, the Matriarch is about to get easier. And I’ll have to start killing that thing.
That brings up an interesting thought. Without thinking about it, I would simply agree with what most everyone said, that with Darken the Skies already played, the mask would not trigger it's effect. However, to remain consistant with this, when the Mask is already in play, it's effect would have to trigger before the text on the just played card is read, another set of fowl cards plus one nonfowl card would be played, and, if applicable, the last nonfowl card played would have it's results before the first nonfowl card played, not counting event effects, although, based on memory alone, she has a small amount of one-shot cards, so the latter situation isn't too likely.