first you need surf a rod any rod apart from old rod then there are only 6 spaces of the 400 squares of water that you can catch feebas but i dont know were they are just surf around and fish randomly hope that helps ! :)
with a pokeball
sex with milotic
feebas can be caught in any waters of route 199.
trade it from ruby or sapphire
Feebas is in the area south from fortree city you must use a rod to catch it.
You can catch feebas everywhere and occasionally barboach i am unsure where to catch magicarp but there is a way
on route 119 u need a super rod to catch it.. and the hardest part is... feebas is only on 6 squares in route 119
In Mt. Coronet, between Eterna City and Celestic town. The water to your right while going to Snowpoint City. Only appears at 4 different tiles. They change daily. If you want to find any more Pokemon or forget where Feebas is go to http://www.psypoke.com/
ok so catch a feebas, which i dontkno how, boost it buety to the max and teach it some good water moves
the rarest Pokemon in Ruby Sapphire and Emerald is Feebas
Actually, it's impossible to catch Milotic in any Pokemon Game. But, it's possible to catch its pre-evolution, Feebas. To catch Feebas in Pokemon Emerald, there is a complicated way. But, I know that you can catch Feebas in Route 119. Hope I helped :)
feebas is the rarest pokemon to catch in a sense. it can be found at the route 119. the road from mauville city to fortree city. surf to the left at the first water that you find after you cross the tall grasses. there will be a trainer that uses feebas. then surf and fish on the water. 5 times on each spot until you find feebas. when you found 1 then there is its nest. just stay on the same spot and capture a dozens of feebas.