Woah, I heard about this super rare dragon bolt that is near the Old Chateux in Pokemon Diamond, unfortunately I haven't found it yet but it is near a entrance in the Eterna Forest!
no
Magikarp
the Pokemon in diamond are sinnoh Pokemon i suggest http://Pokemon.marriland.com/diamond_pearl/pokedex to see all of them
in the old games of pokemon
only magicarp
In Pokemon Diamond/Pearl, you find a old man at route 212 with a Leafeon.
10 years old
The old chateau is in diamond and pearl
the old chateu is only in Pokemon diamond pearl and platinum versions
ROTOM! you can find the plasma Pokemon in the tv of the old chateau!!!
Yes quite a lot of them
underground, they are rare.