there are three ways i will list them easiest to hardest
1)trade it from Pokemon ruby if possible
2)finish the game then go to the weather institute, the scientist dude will say there is a place that is extremely sunny, go there fast or the location will change and you will have to go back to the institute, once there look for a cave that isn't normally there, this is the Terra Cave, GROUDON is in it
3) hack
masterball
Probably trade with Ruby.
The easiest way to catch all the Pokemon is to start with the Pokemon with the lower levels and continue until you reach the highest leveled ones(which is rayquaza, kyogre, groudon and maybe latios OR latias
The only way is if you saved your game before attempting to capture it and if you failed you can reset the game and try again other than that its not possible to retry catching groudon you can however take a groudon from emerald if you failed to catch it or another ruby game. So, no.
Umm... Trade from someone in Pokemon Ruby or Sapphire. In Ruby and Sapphire, you can find Meditite at Mt. Pyre. But, in Emerald, you have to trade it...
Migrate a level 100 Groudon from Emerald or Ruby is the only way I know of.
There is no easy way, you must go to Sky Pillar and reach the top. I advice watching a video walkthrough. ~ James
Weaken it to red hp, paralyze it then use many net balls or ultra balls.
You can't get a Groudon in Pokemon Sapphire, only Kyogre. You can trade your Groudon from your Emerald, and that is the only way, unless a cheating device is used.
you cant catch it the only way to get is to trade it from a ruby
1) complete game then go to the sky pillar and catch it at the top floor 2) trade for it with friends, family, etc. 3) hack
migrate it from emerald