Book of a Thousand Creatures

You can't cast Instants or sorcery spells.
{4},{t}:Add{w}{u}{b}{r}{g}. When you cast your next creature this turn, exile cards from the
top of your library until you exile a creature card with lesser mana value. Until end of
turn, you may cast that card without paying
its mana cost. Put each other card exiled
this way on the bottom of your library in a
random order.