Overseer's Conclusion

Upgrade {x} (You may cast this creature for its upgrade cost. If you do, search your library for a creature card with the same casting cost as this card's upgrade cost, and exile it, then shuffle your library. When this creature dies, put the card that was exiled with this card onto the battlefield.)
When Overseer's Conclusion enters the battlefield, if you cast it for it's upgrade cost, you may pay {x}. If you do, when Overseer's Conclusion dies, return it to your hand.