Cubone is a solid pick, it learns false swipe naturally which can be very helpful.
Axew would be a solid pick for type coverage, it's resistant to everything cubone is weak to. Scyther less so, but it doesn't seem to stop Vinom's character from having one, and nothing has been said about it. But Duskull is also very thematic to your character, so it's a tricky pick. It also has phasing AND invisibility, which if used as a possession target, can be a very effective spy platform.