Collector Ooze

Convoke (Your creatures can help cast this spell.
Each creature you tap while casting this spell pays for
{1} or one mana of that creature's color.)
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 of your
library in a random order.)