You need to dig in the underground.
you dont
You can and its fun
In Diamond & Pearl? Impossible without migrating, trading, or Action Replaying.
in a fossil
You can't without trading, migrating or, cheats
You don't. Its not possible
You can't get diagla in Pokemon pearl without trading but the way to get him in the pearl pokedex is by going to celestic town and going into the big house and talk to the old lady. Only AFTER you beat the Elite four.
Trading, Migrating, Catching the legit legendary Pokemon in pearl, etc.
it is not possible to get them without evolving or trading.
you cant get every legendary of Pokemon without cheats or migrating and trading with people
You mean Dialga? its impossible to find without cheats or trading sadly
Without trading or cheating, you can't. It's a Pearl exclusive.