Jadelight Spelunker is a rare Creature — Merfolk Scout card from The Lost Caverns of Ixalan Promos (PLCI), collector number 196p. Current market price: $0.35 (foil $0.70), TCGplayer market prices via Scryfall.
When this creature enters, it explores X times. (To have it explore, 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 that creature, then put the card back or put it into your graveyard.)