Sinuous Benthisaur is a uncommon Creature — Dinosaur card from The Lost Caverns of Ixalan (LCI), collector number 76. Current market price: $0.14 (foil $0.20), TCGplayer market prices via Scryfall.
When this creature enters, look at the top X cards of your library, where X is the number of Caves you control plus the number of Cave cards in your graveyard. Put two of those cards into your hand and the rest on the bottom of your library in a random order.