Ainulindalë, Song of Life

Whenever you cast a spell, you may pay {2}. If you do, that spell gains Cascade. (When you cast that 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.)
"All have their worth and each contributes to the worth of the others."