It is only possible by cheating.Not by regular gameplay.
The Regis are only obtainable in Diamond, Pearl, and Platinum through trading. They are not found naturally in the Sinnoh region.
you cant it one of the few that you cant catch without migrating or trading
Battle Every single trainer that you come across Walk around in tall grass go to safari zone and catch some Pokemon that's mostly it Enjoy =]
You cannot catch totodile, chikorita, or cyndiquil without migrating.
In Pokemon diamond you can catch Dialga, Azelf, Uxie, Mesprit, Cresselia and Arceus
no
In Diamond & Pearl? Impossible without migrating, trading, or Action Replaying.
Mew and Mewtwo are not found anywhere in the Sinnoh region.
You don't.
You Can not
no
Safari zone
you can't catch it until you don't have a gameshark because its impossible to catch without gameshark