1 May 2012
If the card has {X} in its mana cost, you must choose 0 as its value.
1 May 2012
If the revealed card is a creature card that shares a creature type with a creature you control, but you choose not to cast it, it's put on the bottom of your library. (This is a recent change.)
1 May 2012
If you cast a card "without paying its mana cost," you can't pay any alternative costs. You can pay additional costs, such as kicker costs. If the card has mandatory additional costs, you must pay those.