You need a Pokemon that can use move like mean look or a Pokemon that has an ability, for example shadow tag or area trap. those three things will keep latias/latios from fleeing. (otherwise just use masterball)
P.S. DO NOT PUT LATIAS/LATIOS ASLEEP IT WILL STILL BE ABLE TO FLEE
Ruby cannot capture latias only sapphire and emerald can.
there is no way to capture latias and latios in Pokemon pearl except if you migrate them from other Generation 3.
Capture either a latios or latias
You cannot capture Latias before defeating the Elite Four and the Champion. You will need to use the GameShark to do this. If you are playing Pokemon Ruby, then an Eon Ticket is required to capture her on Southern Island.
You can only capture one of them but of course you can have both by trading.
only latios and latias
You can catch Kyogre, Raquaza, Regice, Registeel, Regirock and Latios or Latias. To capture Latias or Latios, i recommend that you save your master ball cuz' they will run away and it will be difficult to find them again. Wacth the t.v. after you defeat the elite 4. it should ask say that something was seen flying over hoenn and then it will ask you : blue or red pick blue, and you can capture latios pick red, and you can capture latias
The only way to obtain a Latias in Pokemon Diamond is to have it migrated. Latias is not a Pokemon that is encountered naturally in that particular game. The only game that does have Latias is Sapphire version (which can trade to other games, respectively). Thus, to have a Latias in your game, you must either use a cheat code or migrate it and re-capture it in the Pal Park.
Get a pokemon around level 30+ but below 40 leading the party. You have to have beaten the elite four. Next, use a max repel. Go through about 15 patches of grass. If latias hasn't appeared, go to a different route or town and come back. Repeat this process until you find latias. You can't get latias if you have latios.
Of course not. You'll be able to battle it without it fleeing until you defeat it or capture it.
You randomly find Latias in Sapphire version. If you don't catch it the first time you see it, you can go to your poke'dex, select Latias, then chose area and it will show you where Latias is. But, you must get there quick because it could go somewhere else if you are too slow. It gets annoying after a while so be sure to g fast. Also, say the first time you find Latias you burn it, then it flees, the second time you find it, Latias will still be burned. So just keep hurting and chasing Latias until you can catch it. However, you can't find Latios in Sapphire version.
Latias is located on Map 6, though it is only able for capture after you have defeated all Gym Leaders and members of the Elite Four. It is an extremely rare Pokémon, so, naturally, encountering it will be difficult. However, it is always there, so keep looking!