Things You'll Need
Instructions
Play through the game's storyline until you confront Team Magma at Mt. Pyre. The encounter with Team Magma at Mt. Pyre occurs after you enter Lillycove City for the first time.
Defeat the three members of Team Magma, and watch the cutscene. Team Magma will escape and leave behind the Red Orb, which you will then receive.
Travel to Sootpolis City and enter the Cave of Origin. Activate "Flash" to light up the cave. Save your game before you fight Groudon; you may need to reload if you are not able to capture him or if you accidentally kill him.
Attack Groudon with a move that inflicts Sleep, such as Hypnosis, as soon as the fight begins. Avoid using powerful Water- or Grass-type moves. Groudon is a Ground-type Pokemon and is weak to them.
Battle Groudon until his health is low. A quick but risky way to weaken Groudon is to strike him with a medium-strength Water attack such as Water Gun or Grass attack such as Vine Whip. These attacks aren't strong enough to kill Groudon in one hit, but they will bring down his health substantially.
Throw Ultra Balls at Groudon when his health is low. If Groudon keeps breaking out of the balls, try putting him to sleep to make him easier to catch. Throw Timer Balls if you run out of Ultra Balls.