That question was answered many times, except the question was never asked. There are still millions of Pokemon left to be discovered, and you just have to find them. In other words, you will never know how many legendary Pokemon there are until you finish the entire game. (Which took me a few days to finish!)
There are many lengendary Pokemon! There are a lot of other lengend Pokemon when you have the national pokedex!
cheats
you go to the spear pillar.
it would probably be shaymin because he's low level
Pokemon Diamond was released a tiny bit earlier as it is put first in bulbapedia lists and the creators needed time to change the lengendary from dialga to palkia.
You will need to catch the three lake lengendary pokemon. (Mesprit, Uxie, Azelf).
yes sort of
No.
If you want to transfer a Pokemon to Pokemon Diamond and Pearl, you will need Nintendo Wi-Fi. You have to download the mission(s) and transfer to your DS Card.
the lengendary birds are in caves ex. moltres is at mt. ember and the ground lengendary Pokemon pop out of the grass once in the game. it depends on what your starter Pokemon is to what lengendary ground Pokemon you'll get.
no, but it is awsome!!!
no they cant
Yes. You can. However, you must have traded it from another game. I have about three Rayquazas on my Pokemon Diamond because I have traded them there from all the Sapphire games I have restarted.