Merrow Harbinger is a uncommon Creature — Merfolk Wizard card from Lorwyn (LRW), collector number 73. Current market price: $2.77 (foil $9.63), TCGplayer market prices via Scryfall.
Islandwalk (This creature can't be blocked as long as defending player controls an Island.) When this creature enters, you may search your library for a Merfolk card, reveal it, then shuffle and put that card on top.