Oh! Well, it was a Pure Typed 'mon, not a Physical Type, and neither a Starter type nor a type hit SE by a starter type. That leaves only Fairy, Dark, and Psychic as possible options. From there, I narrowed it down to just Uxie and Azelf by taking all the pure type Psychic/Fairy/Dark Pokemon and checking if they had circular eyes and a torso that didn't match their Pokedex color.