Yuxi, Mesprit, and Azelf are some of the many Legendary Pokémon that can be caught in the Pokemon Omega Ruby and Alpha Sapphire games. Read on to find out how to catch these Lake Trio Pokémon.
Steps

Step 1. Get Yon Flute
It can be obtained after completing the Primal Groudon / Kyogre storyline in the city of Sutopolis.

Step 2. Take the three Pokémon with the highest happiness score with you
You can find out the current happiness of Pokémon from the corresponding evaluator in the cities of Verdanturf and Pasifidlog.

Step 3. Use Yon Flute to summon Latios / Latias and fly into the sky

Step 4. Fly to Sutopolis
Near the city, you will find the Nameless Cave. Land here.

Step 5. Inside the cave, you will find a portal
Use the portal and, depending on the time, Yuxi, Mespirt or Azelf will attack you. Yuxi spawns from 20:00 to 21:00, Azelf from 21:00 to 3:59, and Mesprit from 4:00 to 19:59.
Advice
- Save your game before the battle. If a Pokémon accidentally loses consciousness or escapes from the Poké Ball, restart the game and try again.
- Take a Pokémon with an ability that allows you to inflict a negative status, such as Sleep or Paralysis. If you apply negative status, it will be easier for you to catch the Pokémon.
- Take a lot of ultraballs with you. You should also stock up on duskballs if you play at night. You can also switch and use the timer balls.
- Press the B button to fly faster.
- Each Lake Trio Pokémon is level 50, so take Pokémon at least that level with you.
Warnings
- Do not reset the time on the console, otherwise all temporary events will stop for a period of 24 hours.
- During the flight, you may encounter a Rufflet.