You will obtain the Clear Bell from Captain Stern in Slateport City after giving him the Scanner. You can use the Clear Bell key item to find Ho-Oh at Sea Mauville, and this item is exclusive to Omega Ruby.
As for prerequisites, you’ll just need to clear the following requirements before you can get the Clear Bell:
- Beat the Sootopolis Gym
- Obtain the National Pokédex from Professor Birch in Littleroot Town
- Get the Scanner in Sea Mauville
Obtaining the Clear Bell (Step-by-Step)
Once you get the Scanner, fly back to Slateport City to get started.
Step 1: Go to the right of the Pokémon Center and head north, along the main street.
Step 2: Still going along the main street, turn right once you move past the Poké Mart.
Step 3: Continue going right until you arrive at the harbor. Enter the building.
Step 4: Inside the harbor, head over to the left side of the building until you find Captain Stern.
Step 5: Talk to Captain Stern and hand the Scanner over to him.
Step 6: He will give you the Clear Bell in return.
Using the Clear Bell to Find Ho-Oh
With the Clear Bell, you will be able to find Ho-Oh at Sea Mauville.
We’ll also cover this process step-by-step:
Step 1: After obtaining the Clear Bell, fly over to Sea Mauville.
Step 2: Use Surf and head over to the half-sunken platform.
Step 3: Disembark and climb up the ramp.
Step 4: Once you reach the end of the ramp, continue towards the northeast corner of the platform.
Step 5: Keep heading to the northeast until you see a metal beam coming out of the ship. Climb up that metal beam.
Step 6: Continue until the end of the metal beam and you will find a portal. Keep heading towards the portal and you will automatically interact with it.
Step 7: Choose “Yes” when the dialog box appears, and then Ho-Oh will spawn.
Tip: Fighting Ho-Oh during the night gives you a better chance of catching it. Because Dusk Balls will have a better catch rate (3.5x) compared to the Ultra Ball (2x).
What If I Accidentally Beat Ho-Oh?
If you fail to catch Ho-Oh and accidentally knock it out, just fight the Elite Four to get another chance.
Ho-Oh will reappear at Sea Mauville every time you defeat the Elite Four in Omega Ruby.
You can repeat the process as many times as necessary until you catch the Legendary Pokémon.