A Repeat Ball.
Simple weaken it to red HP then use a move to make it sleep constantly throw pokeballs until you get it.
You should use a master ball.
You should use a Master Ball or a ton of Ultra Balls and you might get lucky.
Dusk balls
I captured mine with a poke ball use a weavile false swipe then use gengar hypnosics
you can use master ball in caught the groudon
Ultra ball weaken it to red the easiest way is the dusk ball
go to the eight town and use master ball
you have a special poke ball ( NOT ON THE GAME) which you can buy in toys R us and then connect it to your game then you can put Pokemon into you poke ball from your game and then you it will count how many steps you do and should make you Pokemon in the poke ball fitter (Hope this helps)
The best ball to catch Deoxys is a Master Ball or a Timer Ball! Trust Me!!! Pokemon Master
U can use a poke ball,mega ball,ultra ball but try it from the first when it appear with a quick ball it can catch it faster.
use a master ball