Its simple just get atleast 5 gym badges and go to petalburg city Pokemon center there will be a man next the PC talk to him and he will ask for your new profile type in Mystery event is exciting if it works you are now a member of of mystery events !
I hav'nt played this game in a while but i think its on the bottom floor of the lilycove department store. hope i helped.
I am pretty sure you get a masterball.
Lilycove City.
You're able to play the lottery once a day.
once a day
Pokemon Lottery in Lilycove Dept. store, team magma/team aqua hideout.
In lilycove dempartment store lottery, 2nd prize
In Pokemon Ruby/Sapphire/Emerald you go to the PokeMart building in Lilycove city to try the lottery once a day. It depends on your Pokemon ID number. You get better chances of winning by trading Pokemon with various people. First Prize is a Master Ball.
you can get a master ball by winning the lottery in lilycove
the lotory corner is in the lilycove department store. 1st floor, counter on the right.
You can't, you only get one, though Sapphire/Ruby/Emerald has a lottery where you can get one.
It can be found at team aqua's base also you can win one from the lottery in the lilycove dept store.
I believe you win the lottery. The I.D. number must match perfectly.