Well, I'd make it a possessed doll, but they dropped that opportunity with Banette. They could still use a possessed animal though, something like actually making good use of alternate forms like they did with Darmanitan. It'd be something like Normal/Fairy in its original form and Normal/Ghost in its haunted form. I'm thinking something like a paranoid looking cute animal with his Special Aef and HP that swaps it out for Special Att and Speed when swapping forms. Have it Dr Jekyll and Mr Hyde themed maybe, where it's always paranoid of transforming and constantly has the voice of the ghost in the back of its head.
Alternatively, a Werewolf Pokemon that changes from Fairy to Dark at night or morning. I wish they did more cool things with forms than just tack them on to legendaries as design #2. Deoxys, Kyurem, and Meloetta were okay concepts though, I guess.
