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The closest thing we'll ever get to the mysterious, long-forgotten Gorochu is coming to Pokémon Legends Z-A, but you'll need the paid DLC
Mega Dimensions brings Mega Raichu X and Y, which are curiously reminiscent of the cut Raichu evolution from way back in gen 1.
Raichu was, a very long time ago in the original, first-generation games of Pokémon Red, Blue and Green, set to have a standard evolution of its own. Nishida, who is extremely publicity-averse (in this video interview she spent the whole thing hiding behind a Pikachu plush), spoke alongside fellow developer Koji Nishino, the man responsible for hiding Pikachu behind super-low spawn rates in Viridian Forest because he liked the design so much, and legendary Pokémon co-creator and lead creature designer Ken Sugimori. In fact, their existence makes the likelihood of anything ever known as Gorochu - a name, like Pikachu and Raichu, that comes from combining the Japanese onomatopoeia terms of thunder and a mouse's squeak - even less likely.
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