Pikachu Obliterates a Gym Leader in One Shot 

Ash chooses to take on Wattson, the Hoenn gym leader and expert in Electric Pokémon, in the episode "What's with Wattson?"

While exploring Wattson's gym, Ash and Pikachu see a robotic Raikou, which Pikachu tries to assault and short circuit.

But when they confront Wattson, Pikachu quickly dispatches every Pokémon in Wattson's arsenal in a single blow, stunneing Wattson as well as Ash.

Ash finds that Pikachu's electric power was overloaded due to the Raikou event, making it significantly more potent than usual at the Pokémon Center. 

Ash regrets giving Wattson such a hard time because he is so unhappy over losing so easily.

Ash provides an explanation for what took place, but Wattson still allows him to keep the badge.

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