Instructions
Activating Latios
Travel to Vermillion City, which is south on Route 6 and west on Route 11.
Enter the Pokemon Fan Club, which is located north of the gym.
Speak with the man on the table. He'll give you a Clefairy Doll.
Exit the building. On your way out, Steven Stone tells you that the Latios is loose in Kanto. From this point on, the Latios freely roams the region.
Capturing Latios
Place a Pokemon with the ability to trap or entangle an enemy at the head of your party. Wobbuffet and Gengar both do well. If you do entrap the Latios, it will escape in the first round.
Open your Pokegear Map. It shows you where in Kanto the Latios is currently located.
Travel to the Latios' location. When you arrive, check your map again. If the Latios has moved, go to its new location.
Wander around Latios' location until you encounter him in a random battle.
Use Mean Look or another entrapment skill. Attack Latios until its health is yellow or red. Throw pokeballs at it until you capture it.