yes a level 59 combusken also a level 45 Kyorugre
No.
No, you do not have to beat the Elite 4 to get the National Dex in Pokémon Diamond.
Just train pokemon until you are strong enough to beat her.
It is possible if it's strong enough and has the right moves.
Beat Cynthia after Elite Four
the credits start
After you beat the elite four.
You can get them by winning contests or you can beat the elite four
-mongmong908
beat the elite 4 dips hit
beaten down by close combat!
finish the nation pokedex