Risen Reef is a uncommon Creature — Elemental card from The List (PLST), collector number M20-217. Current market price: $0.40, TCGplayer market prices via Scryfall.
Whenever this creature or another Elemental you control enters, look at the top card of your library. If it's a land card, you may put it onto the battlefield tapped. If you don't put the card onto the battlefield, put it into your hand.