Vodalian Glutton

Players may only spend colorless mana and/or
colored mana that shares a color with the last
colored spell they've cast this turn to cast a spell
unless they exile a card from their hand that
shares a color with that spell.
{u}{b}, {t}: Choose a color. For each spell of the
chosen color on the stack, each player mills two
cards and loses 2 life. (They put the top two cards of
their library into their graveyard.)