Pokémon: Battling the Enemy Within

Animated series. Ash and Pikachu return to the Kanto region to complete the Battle Frontier. Ash and friends finally arrive at the Battle Pyramid. As they get close, they fall into some ancient ruins and are nearly crushed. Then they run into a guy called Brandon who owns a Regirock! Brandon tells them that these are the ruins of the ancient empire Pokelantis. When they find the throne room, Ash touches a sphere and is possessed by the spirit of Pokelantis's evil King.