Black Sludgein Pokémon Polished Crystal

Restores HP for Poison-types, damages others. (Hold) Leftovers but only for Poison-types. Heals 1/16th HP per turn. Non-Poison types take damage instead. Technically better than Leftovers on Poison-types because if someone Tricks it off you, they're stuck with an item that hurts them. Minor edge case, but it's there!