first you link you will need two game boy's and link it to any family or friends until you get inuf.
you have to trade a Pokemon holding it to your game
Lots of ultra balls to catch it, a Pokemon around level 50, Pokemon that know surf and strength.
You can only get lots of master balls by using a cheat/code. There is only one or two in the actual game
u can only get one master ball in Pokemon Black to my knowledge, unless u trade with someone whose Pokemon is holding a master ball, or if u hack it, which there is no hack to.
save your master ball or get a tag from wabafet and give it to a Pokemon with strong light and has a par move or sleep move and get get him to red life and get lots of ultra balls ^u can try that but what i did was i would do is on fire red get a master ball from saffron city at the big building then make a Pokemon hold the master ball then trade the Pokemon into leagreen then when ever entei comes CATCH HIM WITH A MASTAAAAHH BAAAALLL!!!!
you need to go to the jublife TV station and talk to the lottery man and to get a Master ball you need to get the exacet same ID.number
You use the cheat.
Either use a masterball(not recommended) or use status effect like sleep or paralysis and LOTS of ultra balls
Find an action replay code and program it, that's how you get many masterballs on Pokemon diamond action REPLAY. ;)
you go to the top floor at the sky pillar on emerald .you will need a macho bike and lots of ultra balls or a master ball
You can buy Game boy Advanced cheat games. You can then Click on the 999 Master balls cheat.
you have to have a R4.Which will give you lots of cheats