This Octillery is a water-type Pokémon owned by Marcellus. Marcellus owns a multitude of them.
After Remoraid battled Misty's Corsola, it evolved into an Octillery. Although Marcellus lost at the Whirl Cup, the other Remoraid couldn't accept Octillery. After Team Rocket stole the Remoraid, Octillery did its best to free Remoraid, who were rescued by the heroes. The Remoraid evolved into Octillery, pleasing the other one.