now, to catch them u must finish the pokemon league then aftawards, you will go back to ur home then mom says that a thing was flying above hoeen and he askes if you see it and wat color was it Now LISTEN CAREFULLY(most incidents happen here)because if u want to catch latios you need to choose blue and if u want to catch latias, choose red now afterwards go around the hooen region few times(no matter if it is on water or land)until u meet latios/latias, now it is ok for the first time u meet it because it will flee if your pokemon or u havent use a move or something that prevents fleeing because the most important bit is that u MET the pokemon so you can track it down but people have been complaining that latias/latios is moving in different places so here is the VERY IMPORTANT BIT.go to these places that are usually where they are:
1.route 119(anywhere that is on route 119 next to a SECRET BASE)
2.route 120(anywhere that is on route 119 next to a SECRET BASE)
3.route 121(near the sign whch says route 121 so you can switch around route 120 and 121)
afterwards use seccret power on the bushes(except route 121 only first 2 routes)then go in and go out of your secret base and check your pokedex on latias/latios(its at the bottom of pokedex)and look at ther area and if they are not in ur area, repeat the following again until they are in your area(once you are indoors, no matter a cave or buliding, they change area but if you go out or fly or go out in to a different route, they will change too).
The offical tips for catching them(in order)
1.repel doesent work on legendary pokemon
the best way to encounter them is to use a repel because it repels pokemon but it still lets legendry pokemon appear.
now to catch it,get a really strong wynaut or wobbefet because it has shadow tag(trapinch's arena trap doesnt work because it cannot prevent pokemon from fleeing with levitate ablity which latias or latios have)or get crobat because it can use mean look and a good speed so at first, use mirror coat if you got a wynaut or wobbutffet. then eventually latias/latios will use a pshiycal attack(not psyhic attack like futre sight etc.)then they might do damage that does a quarter dameage to ur pokemon then it will use mirror coat the it will do lots of damage to it until its hp its red(dont worry u wont kill it)then start throwing poke balls at it.
dont save the game unless it is captured cos you only get one chance and if your pokemon(wynaut,wobbefut,crobat)died and the latias/latios fled, dont worry, next time u encounter it the hp is the remaining hp from last battles so next time, keep throeing balls at it.
this is real so trust me plz!!
Brandon, pokemon emerald master