When you beat the Elite Four, you will hear about a flying Pokemon over Hoenn. If you have Ruby Version, this Pokemon will be Latios. If you have Sapphire Version, this Pokemon will be Latias. They appear randomly in the grass, and keep the damage you inflict on them (like the legendary Pokemon in Gold and Silver). Once you see Latios or Latias once, you can look for them using the Pokedex. However, they move locations every time you enter a new building, town, or route. Good luck!!!
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