Big problem here is that if you can see the opponent's last card in hand, it's guaranteed instant win. That might not be a huge problem? But it's a natural situation for a discard-heavy deck to start off with nonspecific discard (Cry of Contrition etc), then move on to multi-discard (Mind Rot) or chosen-discard (Coercion). And if I Coercion you one round down from 2 to 1 cards, then you draw and play the card you just drew, I know this can hit. Similarly using Seer's Vision or whatever.

It's the same problem that Cursed Scroll had. With more than one card, it's an interesting guessing game. But it's degenerate with one card. Maybe this should say "If target player has at least two cards in hand"?

I want you to be able to stack the deck to a certain extent, but not quite so obviously. "if they have more than one card in hand" makes sense, but is a bit too blatant, maybe something similar?