Wonder Cards on Pokémon Black 2 can only be downloaded to your game while there is an active event distribution going on regardless of the event distribution being a Wi-Fi one or the distribution being held at GameStop or Toy 'R' Us however there are no current events as of April 20, 2013. Event distributions are free to download.
you have to to obtain the Pokemon and delete the wonder card
Im not sure if you ment 'wonder cards' or 'wonder guards', but a wonder guard is when Pokemon can only get hit with super efffective moves such as sheer cold.
The two Mystery Gift options can only be used by hooking up to a machine at a Pokemon event. There is no such thing as a Wonder Gift - there is only Wonder News and Wonder Cards.
die
You are able to get them online to obtain Darkrai.
Because there is!
you use wonder cards
You cannot, for there is no need of one.
Wonder cards are slots of information that tell you when you get a "special" Pokemon. This is, basically, Pokemon from Pokemon Battle Revolution, or Pokemon from Nintendo Events.
you need wonder cards
yes
noo dont be obsured a wonder card is the rarest posibble card to be found it is the most treasured object in the whole of the pokemon world the only way you can earn suvh a powerful card is by beating charizard with magikarp on the pokemon black and white for the nintendo DS.