Serpentine Sisters

Whenever you cast a creature spell, you may pay {g}{g}. If you do, search your library for a creature card with the same converted mana cost and reveal it. Shuffle your library, then put the card on top of it.
Whenever you cast an instant or sorcery spell, you may pay {u}{u}. If you do, search your library for an instant or sorcery card with the same converted mana cost and reveal it. Shuffle your library, then put the card on top of it.