Things You'll Need
Instructions
Travel to the Seafloor Cavern. To get there, use Surf along Mossdeep City's southern coast and head south until you reach a patch of dark water. Enter the patch and use Dive, then follow the path until you find a doorway on the sea floor; enter the cavern and return to the surface.
Make your way to the end of the Seafloor Cavern. Battle wild Pokemon if you choose and defeat any Team Aqua Grunts you encounter along the way. Many of the cavern's pathways are obstructed by rocks and boulders that you can move or crush using Strength and Rock Smash respectively. In some instances, you must push boulders in a certain order to open paths. If you get stuck on one of these puzzles, leave and re-enter the room to reset the boulders. At the end of the cavern, you'll encounter Team Aqua boss Archie.
Defeat Archie in a Pokemon battle. His Pokemon are Mightyena, Crobat, and Sharpedo; use Fighting-type attacks to knock out Mightyena and Lightning-type attacks to get rid of the other two. After winning the battle, a cut scene will show the legendary Pokemon Kyogre coming to life and you will be transported back outside the cavern.
Visit Sootpolis City and enter the Cave of Origin. Surf northwest from your current location until you reach a large white rock structure and use Dive in the dark water. Once underwater, follow the side of the structure until you get to the opening. Enter it and return to the surface. During a cut scene, Steven and Wallace, the town's gym leader, will lead you directly to the Cave of Origin, which you can enter immediately.