what to do after you have beaten the whole game of pokemon black?

Answer 1

Capture all Unova Pokemon

Capture ALL Pokemon (good luck on that one)

Battle with friends

Complete the Entralink missions

Gamesync with the pokemon website

Fight Alder and a stronger Elite Four

*Sadly, there isn't much to do afterwards*

Answer 2

You can try to evolve your trainer ID. In order to do that you will need :

-To finish the game (normally done)

-Raise your tree in the Entralink to level 3, both sides (the fastest way to do it is to complete five times the lot of six missions in a friend's world)

-Get all accessories for the Pokemon music-hall

-Complete the national pokedex

-Win 49 times in the battle subway, or else you will have to redo it from zero. Good luck to beat the champion.

 

If you manage to do all these things, you will end up with a beautiful black ID, alongside with the proof that you rock ^^