Enduring Tenacity is a mythic Enchantment Creature — Snake Glimmer card from Duskmourn: House of Horror (DSK), collector number 400. Current market price: — (foil $205.30), TCGplayer market prices via Scryfall.
Whenever you gain life, target opponent loses that much life. When Enduring Tenacity dies, if it was a creature, return it to the battlefield under its owner's control. It's an enchantment. (It's not a creature.)