How do I catch Latios?

You could catch a Latios with a master ball, but if you used it already you should have a zubat uae mean look so it can't escape. Then attack it lightly so it can have a little damage then use a ultra ball, luxuary, or whatever. You could find it by using a pokemon with sweet scent and do it on the grass. If your pokemon accidently killed it, turn off your game and do the same thing. If it dies it will NOT come back, so it's best you turn off your game if you killed it. You could catch a latia in ruby without cheating by getting an eon ticket and the people could sail you with the ship to the southern island. You don't have to trade to get one. But here is an advice, when you get to the southeren island save your game in case you killed your latias.

Have a Sableye (Trade) and train it to level 45 to learn Mean Look. Find Latios and use Mean Look. Throw ultraballs at Latios.

Well, fisrt get eithe wabafet or whynaut. When you get a wabafet or whynaut, they have a special ability of keeping the foe in battle. Just get a whole teem of strong wabafet, so if one dies, you have a whole teem of them. Latias/latios are stong, but not against spycic types (wabafet). Just chuck a bunch of ultra balls (stock up with about 50, just in case). Just hope it catches it. To get the latias, I'm afraid you have to trade. But wait till you get latios, so it's a fair traid. Besides, you can traid right back once you get its pokedex data><
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No, latios won't come back , and yes it will be gone forever. No you cant catch a latias in ruby you have to trade.