My suggestion: make this an uncommon and increase the cost (15 G would be ideal). It's too powerful for a common. Not only you reverse the effect of any Undead card played at any part of the game as it's cheap and common (and since it's a common, you can do it 2-3 times in a row), you receive a card that will ruin the opponent's whole hand. And that's only in 2 rounds, with abt 10 gems cost and the thing is repeatable since this card is common.
Other than the rarity and cost, this card is a pretty good idea