You have to get all 7 Gym Badges, beat the Elite 4, and defeat the Champion, Cynthia.
I beat the league on Pokemon Diamond version, and there was no cave involved, if that's what you were asking.
You get a legendary pokemon, to level 100 (trade it).
use ground type
First get the national dex then beat th elite4
Ash has 6 Pokemon in Diamond version
catch Dialga and Palkia this is incorrect, you finish the game when you have completed both pokedex + nationaldex.
I dont have pokemon diamond
beat the game and if you did beat the game go into the cave and you will find mew and mewtwo but you can only go into the cave when you have all pokemon What cave? Where is it???
the same way to beat Pokemon PEARL!!!!
u can't get a lvX Pokemon in diamond version
Yes you also need to beat diamond as well.
you need to have the sapphire version in the gameboy slot and the diamond version in the other slot