Marionette
Marionette is DS' Banette.
Personality
Marionette is a rather odd Pokémon, seeming to enjoy pain, seeing other's suffering as mostly a chance to snack on their emotions and not really treating most situations the way most people and Pokémon would.
Abilities in battle
Her ability is Frisk. Her battle style is pretty different from most of DS' other Pokémon, as it relies more on inflicting status conditions and using Trick to take her opponent's items if her ability finds they have something good.
History
It has not been revealed exactly when or how DS got Marionette, only that DS got her as a recently hatched Shuppet.
In the AU
Marionette lived in the wild as a Shuppet in the alternate timeline, having managed to survive in the distorted Sinnoh. After Sinnoh was returned to normal, DS managed to track her down and add her to her team.