You can really use anything. I, personally, lowered its HP and put it to sleep, then caught it with a couple of Ultra Balls.
GS ball
any kind, i used a pokeball
you cant you need to use some kind of pokeball
Any pokeball will do it. The trick is to use a move that stops it from running away and then you can catch it!
about 20
in any version you need a masterball
You just need one of them.
I'm sorry but you need to start from where you last saved and buy a pokeball. it doesn't allow you to catch it otherwise, and if you knock it out then you battle it again and again.
Best conditions are: Paralyze, Poison, or burn him. You can catch him with different types of pokeballs. I caught him with a regular pokeball. You will need atleast 40 pokeball of each type.
You need to have your starter as charmander and beat the elite four
You need to find an apricot and take it to the guy who can make pokeballs and you will get the apricot pokeball which will help you to catch celebi
premier ball at night or pokeball in the morning and in the afternoon masterball