Rare Pokemon come randomly when you're in the grass or cave.
Sorry but you can't catch it in ruby. You canonly catch it in diamond or pearl.
you don't.....you trade them......
You catch them. Or trade for them.
you cannot catch lugia in ruby/sapphire/... you have to trade from fireRed, and leaf green. to get lugia you have to go to navel rock either in emerald, fire red, and leaf green
tropius is a rare pokemon. but you can catch him near the water institute.
You cannot trade Pokemon to Pokemon Colosseum, but you can trade the Lugia you catch to Ruby or Sapphire.
You have to hack to get to Navel Rock. There you can catch Ho-oh and Lugia.
groudor,rayquazza and more
Mt. Pyre, but they are rare, be patient
he is in th routs 124and126 but is a very rare Pokemon to catch
Shroomish is a rare Pokemon in Ruby and Saphire but you can find it in the Petalburg woods.
Yes you can, its rare though. Go to the Petalburg Woods.