How do you get the Pokemon latios on emerald?

Answer 1

You can get Latios after defeating the Elite 4, then when you appear at your house your mom will say that a rare Pokemon has been sighted.... red is for latias, but the one you want you need to answer blue to pick Latios. He will then be randomly flying around the map then.

a trick that works is to go to the Weather Institute, and keep on going in and out of the building slowly a few seconds between... then check your pokadex, you may have to be patient but he will show up in that area after a while.... happy catching!