Dusk balls
A master ball
Well of course master ball if you have it (thats what i used but then again i cheat) But your best bet would be dusk balls since they work better in dark places and giratina is in a cave.
The best ball to catch Deoxys is a Master Ball or a Timer Ball! Trust Me!!! Pokemon Master
You should use a Master Ball or a ton of Ultra Balls and you might get lucky.
A regular pokeball I'm not playing I caught entie with it jk the best one is a master ball but I did catch entie with a poke ball
you catch it with a poke ball
master ball
use a poke ball
with a poke ball
by throwing it
Catch him with the second master ball you get from the guy at the pokemon center at the top after you have traded 50 times
the ultra ball is what i used to catch it...but you could use the master ball after you get it