You have to go to mt cornet through eterna or celistic towns and go up and use defog then go on the water and use a good rod or you could use a super rod but since its a lower lvl u have a smaller chance of finding it but yeah u can use super rods as well.
Then you just feed it dry pokeblocks until it has around 170 beauty or when u look the beauty has to be near the max. Hope i helped. ^_^
Wild Feebas is probably the rarest (non-legendary) Pokemon in the game. It only occurs on four random tiles in a lake in Mount Coronet. Not only that, but the tiles change every day, and are randomised according to an 'in' phrase that you can set in Dewford Town. If you fish on a tile that actually has a Feebas, however, there is a 50-50 chance that you will catch it, so do NOT fish with a good rod, or a super rod, otherwise the tendency is to catch higher ranking fish.
You will have to trade Feebas and have it hold a Prism Scale.
Feebas
you would use a good rod, but its hard to get feebas its location changes in Mt. Coronet
theres a underground lake deep in mt.cornet
you can't just find it you have to evolve a feebas signed:hartm017
58 and 7 quarts
on the left of sunnyshore city. a fisherman has feebas
mt.coronet
in the rsort area
one of the fishermen by sunyshore city has feebas. Try all of them...
fisher man
mt coronet
Most fisherman:D
feebas
feebas
No
super rod
mt corenet