After Ash beat Clay and got his Quake Badge, Ash and co. decide to head to Mistralton City next. Cilan says that to get there they have to get through Chargestone Cave. When they got there, Ash notice Pikachu was beyond tired. The reason was that a Joltik was feeding off Pikachu's electricity, and he's not the only one the Joltik are feeding off, Iris' Emolga and Cilan's Stunfisk (being part electric) are being drained too. And who should they run into but their old friends, Bianca and Professor Juniper, who explains the situation. What could be causing the Joltik and Galvantula to leech off of other Electric-type Pokémon as well as electricity from the Pokémon Center?
Ash after Bianca knocks him into the water, again.
Professor Oak's Live Caster: Beheeyem
Who's That Pokémon?: Dwebble (Japan), Galvantula (U.S.)
The soundtrack title theme used was actually from the same movie of Zoroark: Master of Illusions when Iris and Cilan stopped Team Rocket's vehicle before the Galvantula and Joltik came out to take back their home.
The soundtrack title theme used when the swarms of Galvantula and Joltik surround Team Rocket is the same as that used in the opening of Arceus and the Jewel of Life.