A commission I bought from  Sambaba

Idea for where it came from is long ago on Cinnabar Island in the pokemon mansion, experiments were conducted in cloning Mew. Due to the experiments, many toxic byproducts were made and had to disposed of properly. However there was one large barrel that had a byproduct so toxic, it had no protocol for its disposal

As they were searching for a solution to the problem, the mansion violently shook, as if something attacked it. They went to investigate and found the barrel gone and a large hole in the ceiling. As if something big reached in and grabbed it

Type: Poison

-Ability-
Clear Body: Opponents’ moves which lower this Pokémon’s stats have no effect. However this Pokémon may lower its own stats with its own moves.

-Hidden Ability-
Corrosion: The Pokémon can poison the target even if it's a Steel or Poison type.

Thanks again  Sambaba