望楼
Draw until you have 6 cards in hand.
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When you gain a card, you may reveal this from your hand, to either trash that card or put it onto your deck.
Watchtower is an Action-Reaction card from Prosperity. It is useful in certain engines(engine) and as a defense against many attacks—its Action effect defends against handsize attacks(handsize attack) and its reaction against junking attacks(junking attack). It reacts any time a card is gained, including when you gain one during your or another player's turn, allowing you to trash the card or put it on top of your deck. In some situations this will allow you to use the new card on your current turn (or at least the very next turn).