When Young Witch is one of your 10 kingdom cards you need an extra Kingdom card (the Bane Card) at random with costs 2 or 3 (makes 11 kingdom cards altogether). When your opponent is playing Young Witch and you have this Bane Card (the 11th card you chose before the game) in the hand, you can shot it and you wont get the curse then. Basically its like a Moat for you.