All Pokemon have the same chance to be shiny, which is 1/4096.
However, Feebas only has a 1% chance to spawn in only two spots, so it might be considered the "rarest shiny."
Unfortunately, Feebas is among the rarest Pokémon in Sword & Shield. This Pokémon has a spawn rate of 1% at one of the two fishing spots in the lake by the Professor's house.
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