First, go to the Slateport City Harbor, north of the Pokemon Center. Team Aqua will steal a submarine. Second, defeat Team Aqua in their base. Then you can go to Mossdeep City and challenge Tate and Liza.
if you mean between kyogre and groudon, then the battle in sootopolis.
There are many legendary Pokemon in emerald, such as groudon, rayquaza, groudon, deoxys, and such. Groudon and Kyogre are not available until after beating Wallace, but Rayquaza can be caught right after the major battle between groudon and kyogre.
In Pokemon Ruby and Sapphire there is no battle between Kyogre and Groudon. That is only in Emerald version. Instead the legendary pokemon (in your case Groudon) is inside the cave of origin in Sootopolis City.
groudon is going upto train groudon easier you should put him in the front of you're party and bring him out to battle first and it would be even better to go and battle the Pokemon league, because there you will see high level Pokemon so you're groudon will gaen a lot of e.p. points.
Better is pokemon emerald.you can catch more pokemon-you can catch kyogre and groudon-you can battle with the frontier brains and collect the seven symbols in battle frontier
first you beat the elite 4 then go to meteor falls on route 114, go to steven and battle him, groudon will apear if you beat him
they are enemy since the beginning. haha XD sunlight and rain they cant get along well
As Wallace is the Champion of the Pokemon League in Emerald, you must first: Visit the Sky Pillar and tame Groudon/Kyogre Defeat all 8 Gym Leaders Defeat the Elite 4
You will battle Groudon for your chance to capture it in Pokemon Omega Ruby after gaining more power.
First you try to get groudon and kyogre into battle, when the Pokemon league champion asks you where is rayquazza is, you say it is in sky tower.
Well,actually I think that Pkemon Emerald is the best,because you can catch both Groudon and Kyogre(this is 100% true) and there is a Battle Frontier.
You can go to the battle frontier, catch groudon and kyogre, and go to the secret place in the safari zone where you can catch Pokemon from the johto region.