What you need to do is grab a super rod. It is rare to catch so go out deep.
you can find a feebas in route 118 and 119 but its hard to find
the rarest Pokemon in Ruby Sapphire and Emerald is Feebas
the only way to evolve it is to have the feebas at a high BEAUTY status for Pokemon contests. and the best way to do this is to have a feebas with a MODEST nature.
You must evolve Feebas.
trade it from ruby or sapphire
You battle Kyogre for your chance to capture it in Pokemon Alpha Sapphire after you capture the groudon.
blue pokeblocks to max beauty
Modest is really great!
anytime after beating champ.
you can get feebas on route 119 very rare
uhi8ii9ihih what are the cheat codes to capture all ledgendary pokemons-pokemon sapphire
Feebas cannot be caught in Pokemon LeafGreen. You would have to trade one from Ruby, Sapphire, or Emerald.