From Bulbapedia, the community-driven Pokémon encyclopedia.
Samejima is a member of Team Great Rocket from Template:Card GB 2. He's one of the Trainers at the Colorless Altar.
His deck, Sudden Growth Deck (Japanese: きゅうせいちょうデッキ), focuses on Pokémon. He refuses to duel against the player unless this has four cards of the type he has chosen at that time (he can request either Jigglypuff, Dratini, or Mysterious Fossil cards).
When defeated, he gives out two Psychic Battle booster packs.