in firered, mewtwo in platinum, diamond, and pearl, mesprit those are just suggestions. pick the one you like most
giratina
Master Ball
Mewtwo I guess????
Witchever you want, but you should probably use it on rare or legendary pokemon.
The best ball to catch Deoxys is a Master Ball or a Timer Ball! Trust Me!!! Pokemon Master
if you did not want to use a master ball on a Pokemon you did not want to capture, if you did not save it then you could restart it and still have the ball but you also get in a trade attached to the Pokemon.
You should use it on cresselia or mesprit because they run away
Definitely Thundurus. You can get 2 Master Balls in Black and White. You should save the second one for shinies or event pokemon.
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.
You cannot find a second master ball however you can trade Pokemon to get another Pokemon with a master ball or use an action replay
You should use it on one of the 'roaming' pokemon, like Cresselia in Diamond/Pearl/Platinum.
Use ur master ball only for latios or latias.......since this Pokemon only appears once in the game and also tries to flee!!!!!