Phage the Untouchable is a rare Legendary Creature — Avatar Minion card from Legions (LGN), collector number 78. Current market price: $13.10 (foil $157.43), TCGplayer market prices via Scryfall.
When Phage enters, if you didn't cast it from your hand, you lose the game. Whenever Phage deals combat damage to a creature, destroy that creature. It can't be regenerated. Whenever Phage deals combat damage to a player, that player loses the game.