Nothing significant happens if you beat the Elite 4 three times in Pokemon Diamond, unless you include acquiring huge amounts of money and leveling up your Pokemon a very good amount.
nothing
You have to see (or catch) every poke in the shinno pokedex
You can't. Basically you can try to remember, but other than that, no. Sorry :)
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII dddddddddddddddddddddddddddooooooooooooooooooonnnnnnnnnnnnn tttttttttttttttttttttttt nnnnnnnnnnnnnnnnnnnnnnnnnnnnnoooooooooooooooooooooo
It doesn't matter how many times you beat the elite four, celebi is not going to just appear.
Absolutely Nothing.
After 20 wins, your rival's Pokemon level up.
You can find out how many times you have beaten the Elite Four in Pokemon Diamond by checking your PC in the game.
Beat the elite 4 7 times retards!!!!!!!!!!!!!
Then you beat them 100 times and win :)
nothing
You don't need to defeat the Elite 4 20 times, your rival is at the Fight Area every Saturday.
No there is no secret store I know that for I have beaten the elite four 20 times and have searched every corner of Pokemon diamond's world.
absolutely nothing.
You have to see (or catch) every poke in the shinno pokedex
you can get them after you beat the elite four a hundred times
on Pokemon diamond and pearl,you have to beat the elite four 3 times in platinum you can get a dusclops in the spring path.