Celestine Reef is a common Plane — Luvion card from Planechase Anthology Planes (OPCA), collector number 17. Current market price: $3.21, TCGplayer market prices via Scryfall.
Creatures without flying or islandwalk can't attack. Whenever chaos ensues, until a player planeswalks, you can't lose the game and your opponents can't win the game.