Find Latias in Pokémon Emerald

Want to catch the legendary Latias? Read on!

Steps

Defeat the Elite 4 and become a champion.
You will wake up back at your home after the credits.
Go downstairs to find your mom and dad.
Your dad will give you a ticket and he will go away.
Talk to your mom.
She will talk about a program on TV and ask which color you like better, red or blue.
- If you pick red, you unlock Latias.
- If you pick blue, you unlock Latios.
Once you have picked your color, Latios or Latias will be roaming throughout the Hoenn region in any random patch of grass.
Get a Pokémon that is level 40 in your team and put it at the front of your party.
- Make sure to have a lot Max Repels. This will make it easier to catch Latias/Latios since the only Pokémon you'll encounter while using a Max Repel has to be at a level equal or higher than your first Pokémon.
Go to a location that has a grass and is nearby a door.
- Use the Max Repels and run in the grass. After around 20 seconds, run into the door and back out. Keep doing this until you encounter whichever one you chose.

Wynaut and Wobbuffet have an ability called "Shadow Tag". This prevents Pokémon from fleeing. Have a strong Wynaut or Wobbuffet (Latios/Latias will attack you) first in your team so that you can keep throwing balls at Latios/Latias without them escaping
They can be found anywhere in grass, caves, water. etc.
They appear at Level 40.
Having a Pokémon with Block or Mean Look can help.
Give the quick claw to your Pokémon. Then use 4 irons and 6 zinc and use them on the Pokémon you are going to use against the latias.
Master Ball can be used for trainers who want to catch them quickly. Using a Master Ball is completely optional but is not recommended considering you only get one in the entire game.
Use Fire Spin/Whirlpool on it. Then let your Pokémon using it hold grip claw. Every 5 turns use Fire Spin/Whirlpool so that Latis can't escape.
Wild Latios know Psychic, Luster Purge, Refresh, and Protect
If you encounter them, they will flee on the first turn.
Latios and Latias are Psychic/Dragon type.

Latios and Latias are extremely hard to catch. Don't get frustrated if you can't catch them. It's only a game.
Don't keep chasing after them 24/7. Take a break.