River Herald Guide is a common Creature — Merfolk Scout card from The Lost Caverns of Ixalan (LCI), collector number 209. Current market price: $0.09 (foil $0.18), TCGplayer market prices via Scryfall.
Vigilance When this creature enters, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)