there is some complicated way that i don't know of to do it in the game, but the eaisier way is to get Pokemon colleseum bonus disk and trade it from the bonus disk to your game boy via gamecube-gameboy adapter cable. (the bonus disk is for game cube and provides one jirachi per game. ie: it will supply unlimited jarachis, but only 1 per game cartrage) i have the bonus disk, but i got it at a Nintendo sponsored event and they were giving them away. i don't know where you can find one now.
You need a GameCube,a Nintendo wii will work also,get the Pokemon limited edition Pokemon collasemon extra disk(super rare so good luck with that).Jarachi should be on that,catch it,then get a gameboy to gamecube connectors cable,trade Jarachi for something.(the gameboy to gamecube cord doesn't work with D.S. so you need a gameboy,or a gameboy SP for the cable cord to work.) Or just get a Action RePlay gameboy, a gameshark works too, then get the Wild Pokemon Modifier cheat for Jarachi.
I don't think you can.
You can't catch it but only by Nintendo events or cheats.
upload from a gba event.
You can't get Jarachi in ruby, sapphire, and emerald. It can only be obtained with a gameshark, action replay, another cheat device, or a Nintendo event and there hasn't been one since 2002 as far as I know.
you need a action replay or a Pokemon event
Well there is multiple things you can do.... If you havent already you can catch Groundon and Raquaza. Then there is the Battle Tower. Last but not least you can fly to the moon. But the only way to do that is to catch jarachi and catch 201 pokemon. Note: Flying to the moon takes a VERY long time to do.
i just started but there might be ... with Acton replay
you cant unless you use action reply
You must get it from a Nintendo Event or the Pokemon Colosseum bonus disk.
If you pre ordered Pokemon colosseum you got a bonus disc that you could get jarachi and put it on ruby/sapphire
You can't catch Zekrom in Ruby version.