Groudon keeps using rest and you cant catch him you used your masterball to catch Rayquaza and Rayquaza is to powerfull to even attack Groudon how do you catch Groudon?

you just need to get the master ball off the galactic grunt boss it has a 100% catch rate hope i helped or you can buy lots of ultra then go to terra cave (thats where find and weaken groudon down real low like about its about to faint but dont kill it then try to catch groudon with an ultra ball this will take patience.........lots of patience