The newest Mystery Gift on Pokémon Black is the Keldeo event which will start on August 27, 2012 and will end on October 6, 2012. It'll be available only at GameStop stores, currently only Gamestop stores in the United States. The Keldeo event is exclusive for Pokémon Black and Pokémon White.
You get special Pokemon. For right now, for Pokemon Black and White, you could receive an Darkrai by using Mystery Gift. These special Pokemon are known as Mystery Gift Event Pokemon.
Yes, you can get different Pokemon when they are ready to get from Mystery Gift.
regigas
Yes, Victini is the Mystery Gift you get. Please click on the related question if you need to know how to get the Mystery Gift.
Sadly there aren't any more mystery gifts. I wanted one but found out that diamond is pretty old so if you want a mystery gift head for Pokemon Black or White, the newest games.
On march fourth in pokemon black and white 2.
Well on Pokemon black and white there is a mystery egg event.
When is there going to be a keldeo mystery gift in pokemon black and white.
In july there will be a mystery gift for koletea
No, there hasn't been one.
There is no current mystery gift outside of Japan. (Unless you've entered a tournament recently)
The current mystery gift for Pokemon: Black is Darkrai. On June 10th this will change though. So hurry and obtain your Level 50. Darkrai. It has a good preset.