Watery Grave is a rare Land — Island Swamp card from Guilds of Ravnica Promos (PGRN), collector number 259p. Current market price: $13.40 (foil $11.74), TCGplayer market prices via Scryfall.
({T}: Add {U} or {B}.) As this land enters, you may pay 2 life. If you don't, it enters tapped.