you have to get piplup, prinplup, or empoleon and breed it with a ditto.
the legendary Pokemon in diamond and pearl are dialga and palkia.
No, a Bidoof cannot evolve into any Legendary Pokémon in Diamond.
Heatran
a lot of legendary Pokemon
Dialga
you cant unfourtanately
arceus
you can't catch it because you already beaten the legendary
you can't unless you have AR
no
Empoleon is not a legendary Pokemon. It is the final evolution of Piplup, one of the starter Pokemon in Pokemon Diamond, Pearl, and Platinum.
That would have to be Dialga.