Agatha/Manga/PA/History

Past
When Agatha and Oak were younger, Oak defeated her in the finals for the Pokémon Championship and Agatha met him after the battle and asked why he quit their "research group". He explained that he wanted to create the Pokédex, which she thought was a stupid idea that would never be complete, and a battle ensued. Oak barely won after a battle that lasted several hours, with Agatha swearing a personal vendetta over him and anyone who associates with him.

Agatha debuted in a cameo when talked about his first championship win, which appeared to be against her in the finals.

Agatha was one of the main villains in this chapter; she was one of the Elite Four who tried to destroy most of humanity from their base on Cerise Island.

She was first seen trying to take away Miles after he was defeated by Yellow and the Good Gym Leaders of Kanto. She was then seen in a flashback during the events of the previous chapter where she battled Blue and attempted to kill him by having her Gengar use Dream Eater to suck away his energy. While encased in the Dream Eater's coffin, she told him of her vendetta against Professor Oak and anyone associated with him, which included Blue. He managed to escape with help from his Golduck, and a Haunter she stole from a Trainer named Ivan was also taken back. She then had her Haunter lead an army of Gastly to attack Cerulean City to delay Misty.

She fought and Koga, revealing an Arbok with the ability to change the pattern on its belly and use different corresponding abilities. She decided to divide Koga and Blue using her Arbok's Rock Slide and she had her Golbat attack Blue. While Blue was distracted fighting Golbat, she had her Haunter use  on Blue's eyes, causing temporary blindness. After battling Koga's Arbok for a while Koga started throwing shuriken balls out of nowhere, which Agatha believed was a pitiful attempt to harm her, but was really Koga's attempt to get a Paralyze Heal to Blue. After that Blue rejoined the battle and Koga used his Golbat's to collect his own blood and smeared it on Arbok's pattern, preventing it from changing anymore. While Agatha was presumably beaten, a second Arbok of hers attacked an unknowing Koga from behind, only to be stopped by Blue before it could land a attack. Agatha was subsequently defeated and seemingly vanished after her defeat, but not before she had her Gengar masquerade as Koga and Blue's shadow to slowly drain their energy, which was defeated as well. She then revealed that she was the one controlling the Pokémon armies of her peers by using special wrist bands to control them.

Agatha used the mind-controlling powers of her Pokémon to control Bruno against his will. It is shown that she was the one who also recruited Lorelei by healing her Seel and then figuring out they have a common distaste of humans.