This is how to Catch Groudon, Kyogre, or Rayquaza!
1. You need a lot of money to buy about 99 Ultra Balls. So just keep battling with trainers. You need a masterball for
Rayquaza.
2. You should have about 1 or 2 STRONG pokemon around levels 50-60 for Ruby and Sapphire. For Emerald, 80-100.
3. Save after doing Steps 1 and 2.
4.When you go into battle, try weakening the pokemon. If your Pokemon faints or if the Legendary faints from the attack
Struggle (Except for Rayquaza because you will use the Master BAll and that catches any pokemon without fail), then turn off
your Game and Start from your save point. You should save the game before challenging Rayquaza, Groudon or Kyogre.
5.Sometimes,
during the battle, if you throw an Ultra Ball, it will catch Kyogre and Groudon with one throw. But the chances of that are
very,very small.
Hope this helped!