Lugia

You will find Lugia at Sea Mauville by diving while inside the research facility. But you can only find it in Pokemon Alpha Sapphire version once you have the Tidal Bell.

Step 1: Start by flying to Sea Mauville, then surf to reach the half-sunken platform.

Walk up the ramp at the entrance and turn right once you spot the staff member to enter the research facility.

Step 2: Inside the facility, walk down a bit and then continue left along the wall.

Step 3: While walking along the wall, turn down at the corner and continue down from there.

Step 4: Keep walking down until you reach the water at the end of the hallway, and then use Surf.

Step 5: Surf a short distance and then use Dive on the dive spot.

Step 6: While underwater, head down the ramp.

Step 7: Turn right past the ramp and continue down the second ramp, which leads to the next area.

Step 8: As soon as you enter the new area, you will get a message that the Tidal Bell is reacting to Lugia’s presence.

After that, continue down the ramp on either side.

Step 9: You will spot a portal just past the ramps.

Step 10: You will get a message the moment you approach the portal. Select “Yes” to fight Lugia.