Because of the poisonous nature of this realm, if Falkovnia is razed, all the champions who attacked it that turn must be discarded.
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Wizards of the Coast
Falkovnia is a great realm to have in the front rank. The power of this realm will often discourage an opposing player from attacking, especially knowing that he will need multiple champions to raze the realm.
If an attacker does indeed raze the realm, all of the attacking player's champions who participated in the combat are placed in the discard pile when the realm is razed. If one or more of the attacking champions are already in the discard pile, Abyss or Void when Falkovnia is razed, they will remain there.
This realm is a great edition to a revenge theme deck as well as a Ravenloft world deck. Some other revenge cards you might consider in a deck with Falkovnia are Assassins (221/4th), Lyr of the Mists (23/PO) and Iuz the Evil (167/3rd). Since you plan to lose the combat anyway, the damage inflicted on your opponent will leave him with a hollow victory indeed.