Syr Gawain, the Great

Cascade (When you cast this spell, exile cards from
the top of your library until you exile a nonland card
that costs less. You may cast it without paying its
mana cost. Put the exiled cards on the bottom in a
random order.)
Syr Gawain, the Great enters the battlefield with
a +1/+1 counter on it for each spell cast this turn.
{g}{u}: The next spell you cast this turn has
Cascade.