This walkthrough will guide you through everything you need to know on evolving Feebas into Milotic in Pokemon Brilliant Diamond and Shining Pearl. There are a few prerequisites like Feebas can only be caught from one specific location and a few more that you need to fulfill before you can catch Feebas and then evolve it into Milotic
Where to Find Feebas in Brilliant Diamond and Shining Pearl
Feebas is a hard-to-find Pokemon as it has a low spawn rate and can only be caught from one specific location within the game in a four-square fishing radius that changes daily. Before going out to catch Feebas, make sure you’ve got the Super Rod, Surf, Defog, and Strength HMs. I have provided the link for each article below.
Feebas can only be found by fishing on one of 4 random tiles at a foggy underground lake inside Mt. Coronet. To reach Mt. Coronet, go to Celestic Town and head west to Route 211. Use Defog on the area so that players can properly see all of the tiles. Feebas will only appear when fishing on one specific tile on the Underground Lake. This specific tile is different for each player and random changes daily. You can use the Step Counter app on Poketch to search the exact tile location.
Alternatively to find the exact location:
Head to Jubilife City and go to Jubilife TV Station. Talk to the lady at the front desk and she will offer you to play ‘Pokemon Loterry Corner’, where she will generate five numbers. Make a note of the number, This number is random for everyone. Next, go to the website mentioned below and feed the same lottery where it says “Today Lottery Number:” and click anywhere outside the map to refresh. It will generate red and green tiles on the map. Either both red or green tiles can generate feebas. This means that if one of the red tiles does not give you feebas, both of the green will.
Link: https://lincoln-lm.github.io/JS-Finder/Tools/BDSPFeebas.html
Evolving Feebas into Milotic
Feebas can be evolved into Milotic by increasing its beauty stat by feeding it Dry Poffins. For maximum effectiveness and beauty, use Dry Berries as an ingredient in these Poffins. After cooking Dry Poffins, feed your Feebas these Dry Poffins to enhance their beauty. When its Beauty is at its peak, either use it in battle or feed it a Rare Candy to level it up. It will then evolve into Milotic as soon as it does so.