The only way this card would be useful is if the opponent has uncommon killer cards (e.g. Orc Regiment) and he is about to play them. This means he has already massed a fair amount of resources. So if you replace his hand with Undead, there is a fair chance you are giving him Undead Host, Corpses Behemoth, Undead Cavalry or even powerful Undead rares. How is that making your situation better? It's a nice idea but it's a big gamble and it might not be used widely if implemented. Ofcourse the effect is good compared with rarity and cost of the card, but it's still not very useful. Perhaps restrict the effect to replacing half of opponent's hand with common Undead cards? That way it's still a gamble, but if it works then it's to your favour.