Death's Oasis is a rare Enchantment card from Ikoria: Lair of Behemoths Promos (PIKO), collector number 182p. Current market price: $0.26 (foil $0.35), TCGplayer market prices via Scryfall.
Whenever a nontoken creature you control dies, mill two cards. Then return a creature card with lesser mana value than the creature that died from your graveyard to your hand. {1}, Sacrifice this enchantment: You gain life equal to the greatest mana value among creatures you control.