You will obtain the Latiasite (Alpha Sapphire) or the Latiosite (Omega Ruby) from Steven on Southern Island. This event is part of the main story, which makes the Mega Stone for Latias or Latios unmissable.
Note that each version of the game can only get one of these Mega Stones, so if you want both then you’ll need to trade between versions.
As for prerequisites, you just need to clear these requirements before you can get the Latiasite/Latiosite:
- Beat the Petalburg Gym
- Obtain HM03 Surf
Getting the Latiasite or Latiosite (Step-by-Step)
After you beat the Petalburg Gym, Wally will automatically take you back to Mauville City.
After that event, take the city’s eastern exit to leave Mauville and you will arrive on Route 118.
From that point, here’s how to get your Latias/Latios Mega Stone:
Step 1: Head east from Route 118’s entrance.
Step 2: Continue heading east past the Aroma Lady trainer. Wait for her to face the opposite direction if you want to avoid the battle.
Step 3: Keep going east until you arrive at the beach.
Step 4: Continue east towards the shore and use Surf on the water.
Step 5: On the water, keep surfing east until you reach the shore on the other side.
Step 6: Once you disembark, head southeast on the beach and then continue towards the eastern side.
Step 7: Keep heading east until you reach the end of the beach. Then turn north and head to the area of grass above the beach.
Step 8: You will immediately run into Steven, starting a short dialogue.
The game proceeds automatically from this point.
Step 9: Latios (AS)/Latias (OR) will then appear and a cutscene will play.
Step 10: After the cutscene ends, you will arrive on Southern Island.
From here, head to the north part of the island, up the hill.
Step 11: Continue into the clearing on the north part of the island.
Step 12: Keep going north and you will find Latias (AS) or Latios (OR) at the end of the clearing.
Once you reach the Pokémon, the game will proceed automatically with another cutscene.
Step 13: An evil team Admin will show up with a grunt and challenge you to a doubles battle. Steven will join as your partner with a level 35 Metang.
The evil team members have:
- A level 29 Koffing
- A level 31 Sharpedo/Camerupt
Step 14: After the battle, Latias/Latios will join your party.
Latias and Latios will also have their respective Mega Stone equipped automatically. So this is when you’ll get your Latiasite or Latiosite.
Are Mega Latias/Mega Latios Worth Using?
Yes, Mega Latias and/or Mega Latios are worth using in your playthrough.
They are the second-best Megas available in the main story, behind Mega Blaziken.
Mega Latias has a varied movepool and well-rounded stats, leaning towards defense. Even so, Mega Latias can still be an effective special attacker in a main story playthrough.
These are Mega Latias’ base stats:
Mega Latios also has a wide movepool and very good stats, leaning towards offense. It is one of the best special sweepers for a main story playthrough.
Mega Latios has the following base stats:
Both Mega Latias and Mega Latios are also good options for a single-player playthrough & for competitive teams in Gen 6.
- Mega Latios is usually considered slightly better, and it functions as a special sweeper.
- Mega Latias slides into a support-oriented role with some offensive upside.
- How To Get the Latiasite/Latiosite in Pokémon ORAS