>>36894283Dark Poison
All poison type moves work just like dark type moves, however, In addition to being Super effective on ghost and psychic, they are also super effective on grass and fairy types. If this pokemon uses Toxic, it will poison steel and poison types, Dark types will be uneffected. This Pokemon is also is immune to poison types moves and status.
I saw pic related and thought it looked cool as a dark type, And I imagined it evolving with the poison stone from the 1997 GS demo (it turns the poison stone's poison into darkness). That's how I came up with this ability