Seymour Guado, Maester

Prowess
When Seymour Guado, Maester enters the battlefield, you may pay {x}. If you do, search
your library for a black Eidolon creature card
with converted mana cost X or less and put it
onto the battlefield. Then shuffle your library.
{u}{b}, {t}: Return target Eidolon creature to its
owner's hand. Its owner discards a card.