A Formidable Rival! (Japanese: 油断大敵！？強力ライバル登場Unpreparedness is the Greatest Enemy!? A Formidable Rival Appears) is the twenty-third chapter of the Pokémon Ruby-Sapphire manga.
Plot
Spoiler warning: this article may contain major plot or ending details.
Red and his Pokémon companions are eating at a conveyer-belt sushi restaurant, and Red finds out that his bill is 50,000 yen because he supposedly ate 500 plates of sushi, although he does not remember him or his Pokémon doing so. As he does not have the money to pay for it, he has to work for the restaurant instead to pay it off. After finally leaving the restaurant, he meets Professor Oak, who says it was just a test, since he figured they were just slacking off anyways. He then introduces Red to a new rival, Red (Ruby-Sapphire). Red and his Pokémon are shocked to see a trainer who looks just like him, has the same name, and has the same First partner Pokémon. Professor Oak instructs Red and his Pokémon to teach this new Red (Ruby-Sapphire) to complete the Pokédex, but Red has already lost his Pokédex, so Professor Oak tells him to go back to Pallet Town, making him sad. Desperate to avoid being sent back to Pallet Town, Clefairy disguises itself as a woman serving tea to Professor Oak at the local inn, planning to steal the Professor's Pokédex instead. Red catches him in the act, and the two get into a frantic tug-of-war over the device, they accidentally rip the Pokédex to shreds. An enraged Professor Oak discovers the ruined Pokédex and banishes them back to Pallet Town immediately.
The next morning, Red (Ruby-Sapphire), approaches the group and reveals he found the original missing Pokédex dropped right outside the inn, but the relief is short-lived as Professor Oak appears and demands that Red and his Pokémon fulfill their promise to train Red (Ruby-Sapphire). Clefairy attempts to show off his seniority by demonstrating a basic Pound attack, but Red (Ruby-Sapphire)'s Clefairy overpowers him by executing the same move with a stronger force. Red (Ruby-Sapphire)'s Clefairy then uses Metronome and randomly rolls Hyper Beam, obliterating a nearby mountain in a single shot. Finding out that this new rival Red (Ruby-Sapphire) is already significantly stronger than them, Red and Clefairy realize they have nothing they can teach him.
