Silvergill Mentor is a uncommon Creature — Merfolk Wizard card from Lorwyn Eclipsed (ECL), collector number 403. Current market price: $0.21 (foil $0.56), TCGplayer market prices via Scryfall.
As an additional cost to cast this spell, behold a Merfolk or pay {2}. (To behold a Merfolk, choose a Merfolk you control or reveal a Merfolk card from your hand.) When this creature enters, create a 1/1 white and blue Merfolk creature token.