Pikachu's Precision Spawns a Pokémon Meme
The episode in question is "Riddle Me This!" from the Indigo League show.
Ash is about to face off against Blaine, the leader of the Cinnabar gym, who dispatches Ash's Squirtle quickly with a Ninetales.
Blaine sends out Charizard to replace Rhydon, but the unruly Charizard takes off and is eliminated.
Ash and Pikachu are now up against a Ground-type Rhydon, which isn't supposed to be able to hurt it according to the rules of the game.
Ash shouts, "Pikachu!" The horn!" Pikachu's Thunderbolt hits Rhydon's horn, knocking him out like a lightning rod.
As a tribute to Ash's anime antics, the games later gave Rhydon Lightning Rod, which charges when hit by electric strikes.
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