Mox Moonstone

When Mox Moonstone enters the battlefield,
exile all nonland cards in your hand, then draw
or discard cards until you have three cards in your
hand.
You may cast cards you own in exile if you spend
mana produced by Mox Moonstone to cast them.
{t}: Add one mana of any color. Spend this mana
only to cast cards you own in exile.