This concept has been discussed before. Accountability can be an issue. When people draw cards, they tend to just add them to their hand without looking at them. The presence of this card in your deck means that you would have to be extra careful and check your draws before adding them to your hand. While it's not THAT bad, it is still a bit inconvenient and easy to forget.
Also keep in mind that such a reaction would be useless without any drawing cards.
I can't remember if there were other drawbacks...
you may reveal this card
That's why I said that you may reveal the card. Also, I wasn't saying that would be the only thing on the card, it could also have something like +2 cards or something on it (still probably not that great).
Well the concern is that people would have it in their hand, then draw cards into their hand and say, "oops, I reveal this card" when that card wasn't actually drawn. This is less of a concern in informal settings, of course.
Now, you could be strict and not allow them to use the reaction if they forget to draw and check before adding the cards to their hand, but then it feels crappy for the player who legitimately forgets.
I wish I could find the old threads about this.
To be clear, the criticism about "the reaction is useless" is not a dealbreaker of course. Moat's reaction is useless when there are no attacks. It is just something to keep in mind.
