Ben, Champion of Bolas

When Ben, Champion of Bolas enters the
battlefield each opponent exiles cards from the
top of his or her library until he or she exiles a
land card.
{2}{u}{b}{r}{t}: Draw two cards. Then you may
discard a nonland card. When you do exile all
nonland permanents with converted mana cost
equal to the discarded cards converted mana
cost.