I think everyone pretty much agrees with TheJord...
Deceit can be used.
That's Two! is doing the discarding, even though it is giving the Shadow Player a choice about what to discard. It is not going to be discarded otherwise. I only see this type of situation as questionable when it goes something like this:
That's Two! is played, and the cost payed. The Shadow player chooses to discard a card that causes a condition to also be discarded when the orignal card leaves play. Is
Deceit usable? I'd say no, but it's on the same vague level, just leaning the other way (that
deceit can't be used).