after seeing Latios or the other do something like this:
everytime you change the rout/city latios's location will change so
1- go to Mauville City
2- then turn left to Rout 117
3- see if Latios where you are if its not back to the city then back to rout 117 keep doing this until its on rout 117
4- make sure that you have a strong pokemon highest than lv40 has something to make latios asleep
5- make him asleep then hit him until he's red
6- throw 3 to 4 Ultra balls before he wake up and I think you will catch him
p.s u can the city/rout thing every where you want I just said Mauville/rout 177 because I did it there "twice"
I can't remember a thing
latios always fled or does he attack sometimes ?
and I said sleep because that stops the 3 legendary dogs from fleeing , I thought its the same
but the changing rout/city strategy works 100%
So its a bit hard