Get ready to walk another Pokemon in order to evolve it in Pokemon Go.
Pokemon Go's support page revealed that players will need to walk Feebas as a "buddy" Pokemon in order to evolve into Milotic. "Buddy evolutions" are relatively uncommon in Pokemon Go, but it makes sense given that Feebas requires a high "Beauty" condition before it can evolve in the main games.
Feebas is the third Pokemon to require extra attention before it can evolve. Previously, players had to walk an Eevee 10 KM as a buddy in order to trigger its evolution into Espeon or Umbreon. That requirement was meant to mimic the main games' "Friendship" metric, which was first introduced in Pokemon Silver and Gold.
Of course, not every Pokemon that has an unusual method of evolution carried this over into Pokemon Go. Togepi, Chansey, Cleffa, and Golbat also needed high Friendship to evolve in the main series games, but simply need the proper amount of candies in Pokemon Go.
Some thought that Feebas would simply need a new evolutionary item to evolve in the games. Later generations of the Pokemon games, which didn't have a way to improve a Pokemon's "beauty," required Feebas to be traded with a Prism Scale. Some assumed that Pokemon Go would simply add the Prism Scale as a new evolutionary item to go along with Deepsea Scale and Deepsea Tooth, which Pokemon Go also confirmed would soon get added to the game.
Pokemon Go's GAME_MASTER file previously revealed that Feebas also requires 100 candies before it can evolve into Milotic, so players should be ready for a whole lot of walking AND catching before you can add the entrancing Pokemon to your collection.