You can transfer it from an old Pokemon game (such as Pokemon fire red) or trade other people.
no you cannot. unless you go to the special events Nintendo does.
Without trading, cheating, or Nintendo events, you can get Dialga, Uxie, Azelf, Mesprit, Heatran, Giratina, and Cresselia.
no
events
to get Manaphy without cheating, you have to have Pokemon Ranger, beat a certain mission, and then somehow transfer the Manaphy egg to Diamond or Pearl.
Only if you got the event.
You can't
this is impossible without cheating, even with cheating it may not be possible.
You have to mete the Pokemon lots of time, 1 time it will be shine.
definitely a Nintendo event
The Pokemon that can be caught without special events, trading, or cheating in Pokemon diamond are: Uxie Mesprit Azelf Dialga Giratina Heatran
you can't