Level up Feebas with high Beauty/Beauty condition in games where it evolves by Beauty
In Pokémon Ruby, Sapphire, Emerald, Omega Ruby, and Alpha Sapphire, raise Feebas’s Beauty to the required level, then level it up
In Pokémon Sword and Shield, trade Feebas while it is holding a Prism Scale
In Pokémon Brilliant Diamond and Shining Pearl, trade Feebas while it is holding a Prism Scale
In Pokémon Scarlet and Violet, trade Feebas while it is holding a Prism Scale
In Pokémon Legends: Arceus, use a Prism Scale on Feebas
In Pokémon GO, evolve Feebas with 100 Feebas Candy and a special buddy-walking requirement
In games where Feebas can evolve by trade holding Prism Scale, make sure it is holding the item before trading
In games where Feebas evolves by Beauty, maximize Beauty before leveling up