
Don’t forget, it’s not only the future card that you cancel, but the existing card is also removed from the deck while waiting for future nastiness. Some of the nastiest scenarios in the game have ancient evils and the encounter discard pile gets shuffled back into the deck one or more times. So this card takes Ancient evils (or other doom-applying card effects) out, making the encounter deck lovely and cuddly when reshuffled.
I wonder what happens with this card for surge cards. I know you can't cancel the surge, but if its a truly horrible one (say some of the peril surge doom-adding cards early on in The Forgotten Age), then could you discard and cancel the revelation effects of the card with a Ward of Protection, but because the surge keyword does have an effect, you could also play Fool me Once..., to protect against a future version of the card (in the case of a peril card, clearly only works if you are the one to draw it a second time)
If that does count, then you could even play that very same "Fool me once..." again, if you are playing Diana and have the twilight blade in play?
1) Draw the first encounter card (a treachery one) with a surge effect (and a nasty revelation effect). Resolve any effects
2) Play "Fool me once..." and attach the nasty encounter card to it.
... play a few more rounds...
3) Eventually draw a second nasty treachery card of the same type.
4) Trigger the reaction ability on "Fool me once..." - cancel the card's revelation effect.
5) Trigger Diana's ability to put the "Fool me once..." card underneath Diana (draw a card and resource)
6) Resolve the treachery card's surge effect. (note the rules do specifically use the word resolve for the surge keyword)
7) Get to the point where you are about to discard the treachery card in question.
8) Trigger the reaction ability on Twilight Blade to place "Fool me once..." in your play area and attach the treachery to it.
Any thoughts on that ?