Seafloor Cavern & Deep Ocean

1. Descending the Route 128 Trench

When you Surf south from Route 127 onto Route 128, locate the ring-shaped reef enclosing deep navy water and use Dive to submerge into the oceanic trench. Search the submerged rock tiles and the circular sand bank framing the trench to uncover hidden Heart Scales. Swim south along the ocean floor until you spot Submarine Explorer 1 parked outside a cave entryway, then enter the opening and surface with Dive.

Tip: Wild encounters here range from Lv. 28 to 39, so ensure your party can handle unexpected aquatic battles.

2. Entering the Cavern Threshold

After surfacing inside the Seafloor Cavern Entrance, step through to Room 1 to face an inner pool flanked by cracked rocks and Strength boulders leading toward either Room 2 or Room 4. If you have not yet cleared the Mossdeep Space Center, a Team Aqua Grunt will be blocking your forward passage entirely. Once cleared to proceed, push the boulders and smash the breakable rocks to choose your interior route.

Tip: Use Fighting, Electric, Grass, or Psychic moves against any opposing Aqua forces to easily counter their Dark, Water, and Poison types.

3. Navigating the Cavern Rooms

Advance across Rooms 2 through 6, choosing between rushing through the rapid-filled current maze in Rooms 5 and 6 or taking the slower rock-smashing and boulder-pushing corridors. The rapids provide swift transit across the cavern while bypassing certain encounters, whereas the boulder paths demand field moves and pit you against patrolling Team Aqua Grunts. Battle past their squads of Mightyena, Golbat, Poochyena, and Carvanha while remaining alert for Intimidate debuffs and Swagger confusion.

Tip: Equipping your team with Persim or Lum Berries neutralizes troublesome confusion from the enemy grunts' Swagger attacks.

4. Breaching Room 7's Guard Post

Push into Room 7, where a narrow doorway choke-point is guarded by a Team Aqua Grunt alongside Aqua Admin Shelly. Engage Shelly in battle against her Lv. 37 Mightyena and Lv. 38 Sharpedo. Strike her Mightyena with Bug or Fighting attacks, and dismantle Sharpedo with non-contact Electric or Grass moves to avoid Rough Skin recoil while neutralizing its fierce physical offense.

Tip: Bug-type attacks will hit both of Shelly's Dark-type combatants for super-effective damage.

5. Solving the Room 8 Boulder Maze

Enter Room 8 to find a massive triangular Strength boulder formation sealing off the northern entryway. Plan your pushes carefully as you shift the stones out of the way to carve a path through to the far door. Once the way is cleared, step through the north opening into the deepest chamber.

Tip: Take your time tracing each stone's trajectory before using Strength to ensure you do not shut off your own path.

6. The Deepest Cavern and Archie's Awakening

Step into Room 9, head right along the elevated path beside the ramp leading to Kyogre's pool, and collect the Poké Ball containing TM26 (Earthquake) from the floor. Descend to the basin to observe the slumbering ancient leviathan Kyogre before confronting Aqua Leader Archie as he wields the Blue Orb. Topple Archie's team of Mightyena, Crobat, and Sharpedo by targeting their weaknesses with Rock, Ice, Electric, Grass, Bug, or Fighting moves—favoring special attacks like Thunderbolt or Giga Drain on Sharpedo to dodge Rough Skin recoil.

Tip: Crobat is remarkably fast, so have a Rock or Electric specialist ready to exploit its vulnerabilities immediately.

7. Aftermath of the Awakening

After Archie falls and Kyogre awakens, Maxie and the Magma Admins rush in to confront Archie regarding his reckless actions. The awakening triggers extreme regional weather across Hoenn and automatically teleports you out of the cavern, where Steven Stone arrives to direct you toward Sootopolis City. If you left anything behind, note that you are entirely free to return to the Seafloor Cavern via Surf and Dive whenever you wish.

Tip: Steven Stone directs your next objective directly toward Sootopolis City to handle the escalating crisis.

The short version

What matters

• Picking up TM26 (Earthquake) from the floor on the right path in Room 9 before waking Kyogre.
• Using Dive to find hidden Heart Scales scattered along the Route 128 underwater rock tiles and circular sand bank.
• Utilizing special-based Electric and Grass moves like Thunderbolt and Giga Drain against Sharpedo to avoid Rough Skin damage.

Common mistakes

• Shoving a boulder against a wall in the Room 8 triangular puzzle, which blocks the passage and forces an exit and re-entry to reset the room.
• Attempting to explore the trench before completing the Space Center events, causing your path to be blocked by a Team Aqua Grunt.
• Relying on physical contact moves against Shelly's and Archie's Sharpedo, which inflicts Rough Skin recoil damage onto your Pokémon.

What you can skip

• Navigating the tedious rock-smashing corridors in Rooms 2 through 4, or sweeping through the rapid currents of Rooms 5 and 6 if you prefer a faster route.
• Missing certain Team Aqua Grunt encounters if you select the current maze route.