You don't. Pure and simple.
Trade with someone that has Pokemon pearl.
trade with someone that has Pokemon diamond
You need to have Pearl or trade with someone who has Pearl.
No way.... Someone hacked!
Bagon is only available in Pokemon Pearl, but you can obtian it in Pokemon diamond by trading someone who has pearl
There is armour fossil in Pokemon pearl, it is a fossil that has a shieldon in it, or you could trade with someone from diamond for a cranidos.
trade diamond from Pokemon diamond onto Pokemon pearl
You trade Magmar from Pokemon pearl,diamond,or platinum to ether Pokemon pearl,diamond,or platinum.
THE POKEMON THAT ARE NOT FOUND IN DIAMOND AND PEARL ARE:MANAPHY PHIONE
You can get Palkia in Pearl, otherwise you have to transfer Palkia from Pokemon Pearl to Pokemon Diamond.
diamond
obtaining gym badges allows you to control Pokemon within certain lvl ranges