You can either use action replay or it might not work but I'm not sure about the other ways
Weaken it then use many great balls or pokeballs or timerballs if you own a registeel from a friend try using a repeat ball. This is no joke when i tried to catch registeel i already owned one from a friend and i just threw a repeat ball and i caught it on the first try.
use a master ball
I captured Kyogre by weakening it and after using (and failing with) Ultra Balls, I used a Great Ball and caught it.
use master ball, ultra, or great usually, master ball is grater to catch Ho-Oh.
Use Electric Types To Paralyze The Get The Life Low And Use Ultra Or Great Ball.
Weaken him until he's almost fainted, and then inflict a status (sleep preferably, but paralysis, and freezing also work) upon him. Use a ball with a high catch rate (ultra ball, and great ball work well).
u cant u need to catch bonsly which u can only get at the Pokemon manchion by the great marsh and it is rare rrod54 the true Pokemon master
Lower his HP then throw a bunch of great balls and ultra balls. He knows phyco cut,amnesia,guard swap,and power swap.
Bring a ton of Ultra Balls like 50 of them trust me do not use a master ball on him hes not all that great
Throw a master ball at it, or weaken it then throw an ultra,great or pokeball that should do the trick
Although Professor Oak gives you a tutorial at the beginning of the game, all you have to do is attack the Pokemon without making it faint, then throw a pokeball, great ball, ultra ball, or even the master ball at it. You may not catch it on your first try, so don't be discouraged of you fail.
Put its HP down 2 red,(giving it a status problem helps) and use different kinds of balls. I recommend you stock up on ultra, great, and timer balls. Bonye