Beating the elite-4 or catching palkia without a masterball.
Its really hard to get one you might as well check GTS not waste your life....
No Pokemon can evolve with a hard stone
empoleon learns whirpool, and other pokemon. but the whirpools in the sea are hidden really so there hard to spot!
a lot hard
On Diamond and pearl you don't really see many fire Pokemon or electric types. But really the rarest ones are legendarys. Also Garydos is a good Pokemon hard to get without super rod
None
Buneary can be found in the Eterna Forest on Pokemon Pearl. It is rather common and not hard to find.
You fight the Champion. Of course he is really hard... Then you go to Spear Pillar. At Spear Pillar you can catch Palkia.
choose chimchar because you rarely come across strong fire Pokemon in pearl if so very hard to find
train hard with it or give it rare candies to lvl 100.
you can catch dittos in Pokemon diamond and pearl with poke radar in route 218 but its pretty hard to catch them + find them. :)
It is really hard to find them so you need good luck to find a shiny. There is a 1 in 8192 chance of finding a shiny Pokemon in the wild or hatching one from an egg.