Shadow (This creature can block or be blocked by only creatures with shadow.) Whenever Stronghold Rats deals combat damage to a player, each player discards a card.
In the stronghold's dungeons, the shadows hide in the vermin.
Official Rulings for Stronghold Rats
5/1/2007 : First the active player chooses a card to discard, then each other player in turn order chooses, then all cards are discarded simultaneously. Although the chosen cards will be indicated (so a player can't change his or her mind later), they'll remain face down until they're discarded. You won't know what your opponent is going to discard when making your choice.