Treacherous Terrain is a uncommon Sorcery card from The List (PLST), collector number C16-47. Current market price: $0.33, TCGplayer market prices via Scryfall.
Treacherous Terrain deals damage to each opponent equal to the number of lands that player controls. Basic landcycling {2} ({2}, Discard this card: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.)