Feebas
Feebas can only be found on Route 119, and is very hard to find. Feebas only appears in six tiles on the route. The tiles are random, depending on the popular phrase you used in Dewford. Catching this Pokemon requires a lot of time and patience. However, when evolved into Milotic this Pokemon is very useful. To capture Feebas try using "Mudkip Ball" as your popular phrase in Dewford. Later it turns to "Natural Flowers". Wait until "Natural Flowers" is the popular phrase or attempt to change it yourself. To find Feebas, get to Route 119. Start at the bottom and move north. Stop at the first little lake, immediately after the large patch of tall grass, and go as far left on the lake shore as you can. Surf, move one tile north, and fish with a Super Rod. Note: The tile locations may vary from game to game.