Eusine/Manga/GB

Eusine is first seen coming to Cianwood Gym and trying to retrieve a from 🇬🇼. It turns out that this Pikachu was actually a messenger sent from future by Eusine and Bill to guide the present Eusine to Legendary Pokémon using a special learning device attached to it. Gold wanted to battle Eusine for that Pikachu, but Chuck, the Leader of Cianwood Gym, told them to battle next day. Gold and his beat Eusine's Hypno and Gold won the battle, so Pikachu could stay with him. This caused Eusine to search for Legendary Pokémon alone.

Later, 🇬🇼 unsealed the Black Tyranitar, Cianwood's Legendary Pokémon who used to wreak havoc in the Johto region. Eusine was one of the people who helped Gold fighting the Black Tyranitar.