The Black Sludge (Japanese: くろいヘドロBlack Sludge) is a type of held item introduced in Generation IV. It heals the holder if it is Poison-type, but damages the holder otherwise.
If currently held by a Poison-type Pokémon, the holder restores 1/16 of its maximum HP (rounded down, but not less than 1) at the end of each turn.
If currently held by a Pokémon that is not Poison-type, the holder takes damage equal to 1/8 of its maximum HP (rounded down, but not less than 1) at the end of each turn. Pokémon with the AbilityMagic Guard are immune to this damage.
In Generation IV, Black Sludge is able to heal the holder regardless of Heal Block. From Generation V onwards, Black Sludge cannot heal Pokémon affected by Heal Block.