Wave of Change

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.)
As this spell resolves, if you cast a noncreature
spell with converted mana cost less than this
spell's converted mana cost, return it to its
owner's hand at the beginning of the next end
step.