Ah, right, the tracking of different copies of Warden... I understood it as something like:
+1 Card per attack card you revealed a Warden to this turn.
But yes, of course you could technically reveal it multiple times and abuse the card that way. I forgot about this.
ClouduHieh, the rules of Dominion allow you to reveal any Reaction card multiple times to the same attack. It's a bit complicated to explain why, but nonetheless it's allowed. All the real Dominion cards take care that this doesn't make the game unfair: Some simply don't give you anything extra if you reveal it multiple times. Like Moat, because you are either protected from an attack or not, but you can't be protected multiple times... And some Reaction cards simply move themselves away from your hand, so you can only reveal them from your hand once.
The problem is, if Warden makes you draw cards when you reveal it, because the rules allow you to reveal it multiple times, you can use it to draw as many cards as you want.
Here is an idea:
When another player plays an attack card, you may reveal this from your hand. If it is the first time you revealed a Warden to that card, it doesn't affect you, and +1 Card per Attack card the other player has in play.
Sadly,this is a lot of text... Another idea:
When another player plays an attack card, you may set this aside from your hand. If you do, until your next turn, when another player plays an attack card, it doesn't affect you and +1 Card. At the start of your next turn, put this in your hand.
Erm,that's even worse... Maybe a Duration card? This is more tricky than I thought.