Elvish Harbinger is a uncommon Creature — Elf Druid card from Lorwyn (LRW), collector number 207. Current market price: $7.23 (foil $19.73), TCGplayer market prices via Scryfall.
When this creature enters, you may search your library for an Elf card, reveal it, then shuffle and put that card on top. {T}: Add one mana of any color.