Quicksilver Amulet

Oracle Text

4, T: You may put a creature card from your hand onto the battlefield.

Card Rulings

10/4/2004 Any ‘X’ in the creature’s cost is treated as zero.
5/1/2007 Putting the card onto the battlefield is optional. When the ability resolves, you can choose not to.
9/22/2011 You don’t pay any costs of that creature card, including additional costs.