I recommend saving it for mewtwo, in Cerulean cave.
It's a strong Pokemon, and has a high chance of defeating you and a low chance of capture, and you also have to take into concideration that the cave you need to travel through to reach it is very dangerous, with high-level Pokemon; needless to say, your Pokemon will be tired when you fight it.
The best ball to catch Deoxys is a Master Ball or a Timer Ball! Trust Me!!! Pokemon Master
Master Ball
no it won't be holding a master ball cos when you used the master ball to catch a certain Pokemon, the master ball will be gone in your inventory because it is a consumable.
A master ball can catch any wild pokemon.
No.
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
master ball
No
On a certain Pokemon that you want to catch and it's hard to catch it with just a Poke Ball, a Great Ball, or an Ultra Ball. I don't know where else you can get Master Balls besides the Silph Co. I usually use the Masterball on legendery Pokemon.
no
You cant catch any trainers Pokemon
a utra ball or a master ball