RE: The D/P Questions and Answers Thread
Dark Marc: Sorry, I've no clue how to answer that question.
Doc Savage: I may be forgetting a few things, but this is what you can do after getting the National DEX:
-Access Turnback Cave and battle Giratina.
-Have full access to every part of the island north of Sinnoh (for some reason I can't think of its name at the moment... xD), which means Battle Tower and Stark Mountain, to name a few things in the area.
-Pal Park opens up, so you can migrate your Pokémon to your game.
-You can now get Regigigas in Snowpoint Temple if you migrate the three Regis from the older games.
-Swarms will now occur, so be sure to speak to the little girl in your rival's house (well, the other trainer that works for Rowan, not the blonde rival) for details on what's swarming and where.
Like I said, I think I'm missing a few things, but that's pretty much what opens up after getting the National DEX.