Hachirou

Marcellus is a character of the day who appeared in Octillery the Outcast (EP217). He lives in Scarlet City on Red Rock Isle.

Shortly before the Whirl Cup began, Marcellus approached Ash and his friends, requesting a battle. He wanted his Remoraid to evolve into an Octillery so he could have a strong Pokémon for the competition. Misty accepted the challenge and pitted her Corsola against Marcellus's Remoraid. She ended up losing, and Marcellus's Remoraid evolved at the end of the battle.

The next day, after the preliminary qualifying rounds, Ash and the others noticed Marcellus appeared to be sad. He revealed that he lost the preliminaries and was now out of the competition and invited the group over to his house for dinner. That night, he explained the reason why he lost: his tank full of Remoraid had treated his newly-evolved Octillery so differently and so poorly, neither had been able to concentrate on their preliminary battles and had ended up losing because of it.

Team Rocket arrived and stole all of the Remoraid with their vacuum truck. However, Octillery left an ink trail, allowing Marcellus and the others to track the trio down at a port, where they rescued the Remoraid. After saving Octillery from falling, all of the other Remoraid evolved into Octillery themselves and subsequently inducted Octillery back into their group, pleasing Marcellus.

Marcellus was last seen watching the Whirl Cup's stadium empty out its water with Ash, Misty, Brock, and the many trainers who'd made it to the main tournament.

(Source: Bulbapedia)