You need to first weaken it, when its healt bar is red, put it to sleep and use Ultra Balls to try and catch it.
no u can only catch him on emerald
we can catch it by using prof.oaks great ball
rayquaza. use a master ball on it. is very hard to catch using ultra bal even if it is red and has a status prob.
You can't catch Rayquaza in Undella Town or Bay. You'll need to trade for it or transfer it using the Poke Transfer.
get it asleep or paralyse it. then use a ultra ball
you go to relic castle
Use the Master Ball if you need to catch a Pokemon without fail. I'd suggest using it on a legendary, though - don't waste it on a common Pokemon.
It can be if you want it to or you can use it on rayquaza, the easiest way to catch latios or latias without using the masterball is by having a Pokemon that has the abilites: Arena Trap, Shadow Tag and having the Pokemon be sent out first then weaken latios/latias then throw many ultra balls.
Absolutely. It fills up your Pokedex, and if you're using legendaries on your team, it will help you defeat the Elite 4. Just don't waste your Master Ball on it. You're better off using it on the roaming legendaries (Latios and Latias), since they're more difficult to catch.
Nope.
I captured Kyogre by weakening it and after using (and failing with) Ultra Balls, I used a Great Ball and caught it.
All you have to do is use the master ball