cmplete the game and go to each cave and try to catch them
YOU CAN CATCH HIM IN LAKE VALOR.BUT YOU HAVE TO CATCH YOUR REGION POKEMON.(PALKIA OR DIALGA).THEN YOU TRAVEL TO LAKE VALOR AND YOU WILL SEE A CAVERN.THEN YOU WILL SEE AZELF IN THE MIDDLE. JTROTTER1295
To complete the pokedex you only have to see them. However, I would advise capturing them. Azelf has very high attack and speed stats, while Uxie has high Defence and Speed stats. Mesprit is a combination (has around 120 in each stat when you catch it).
uxie groudon mesprite azelf and dialga
The only way you can see all the Pokemon on diamond is by going into the GTS and global trade different Pokemon.
the Pokemon was azelf or it could have been mespert or uxie one of those
you have to catch all of the pokemon in diamond or SEE all of the pokemon
A Pokemon
Yes, but its for platinum only, if u have all the lake pokemons (Mespirt, Uxie, and Azelf) bring 'em to the cave... Click on the etching of the lake pokemon, and a special pokemon will appear, exlusive for Platinum Only
when you do the veilstone building at the end you see and battle cyrus who is keeping mesperit , azelf and uxie in these chamber things ( in another room ) after you defeat him he gives you the master ball hope i helped :P
The Pokemon you see do not go in your pokedex.
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No, you cannot see every Pokémon in the National Dex in Pokémon Diamond however you can see every Pokémon in the regional Sinnoh Dex in Pokémon Diamond.