This is, believe it or not, my first run through of Pokémon Emerald.

I intend to RNG for all of the Legendaries but first I need to make sure that I am able to catch them.

I've spent a while now practice catching Rayquaza without success. I don't want ot use my Master Ball because Groudon will probably be even harder to catch and once I get to the Battle Fronteir I might be able to duplicate some Master Balls for catching the others.

Originally I tried to use the 1HP Endeavour method but it only works 1/3 of the time so isn't ideal for repetitive RNGing.

Then I tried a Shedinja with Spite to get rid of Rest PP and Protect to stop Fly. It had Swords Dance and False Swipe to weaken Rayquaza in the mean time.

Then I realised that this wasn't enough so I replaced Protect with Grudge to get rid of Fly all together but Rest is still a problem. If I get rid of Rest and Fly that means it only has 20PP left meaning I get 20 Pokéballs to throw minus 1 for every turn I spend weakening it (8) then sending it to sleep (2) then putting it to sleep again every time it wakes.

After that I have very little chance when it will take me 30 something Ultra Balls to catch on average.

So what did you all do and do you have any advice?

I've yet to try to catch a legendary more than once (IE, the repetitiveness needed to get a good one, like you're trying). I generally just throw some guys out there, paralyze it, weaken it, etc, and start chucking Ultra Balls.

Personally, you should wait for the Battle Fronteir to clone your master balls. We all know those make catching pokes FAR easier and quicker

But if you REALLY want to catch him now, then here's a few possible tips. You should try paralyzing it first so it will be much slower and occasionaly won't move, and thus buying you more time. I know putting him to sleep is better with the catch rate, but he wakes up quickly. Then use a medium-powered move or two to get his health fairly low, and then use weak attacks/False Swipe to get his health very low. Then start chunking those Ultra Balls. And if you've taken 15 turns in battle (it might be 10 turns, but I'm not sure) then start using some Timer Balls.
And remember: SAVE BEFORE BATTLING!!

Good luck!

Thanks guys. I'm going to try paralysing it.

While trying to catch it Rayquaza got paralysed by Effect Spore and it worked wonders.

I managed to hold off the struggling for ages and it gave me time to use most of my balls.

Also I completely forgot about timer Balls. I forgot they existed in Gen3.

I shoudl have a much better chance now. Thanks.

I usually just weaken it to about low yellow, throw ultras at it, and let luck take care of the rest.