Thunderbolts Conspiracy is a rare Enchantment card from Marvel Super Heroes (MSH), collector number 117. Current market price: $0.28 (foil $0.36), TCGplayer market prices via Scryfall.
Flash Whenever a Villain you control dies, return it to the battlefield under its owner's control with a finality counter on it. That creature is a Hero in addition to its other types. (If a creature with a finality counter on it would die, exile it instead.)