go to pokemon.com and it has all the upcoming events listed with their dates and details
There is Victini, Keledeo, Meloetta, & Genesect
It's an event exclusive Pokemon
there is not going to be an event for arceus on Pokemon black sorry to disapoint you.....!
there will be a next event on pokemon black and white
meloda is an event pokemon, the date of the event is unknown
in an event
There are Victini (Event), Virizion, Cobalion, Terrakion, Tornadus (From Pokemon Black), Thundurus, Landorus, Reshiram (From Pokemon Black), Zekrom, Kyurem, Meloetta (Event), Keldeo (Event), and Genesect (Event).
It is an event pokemon, the event for which has not been run yet.
The only way so far is to cheat via the Action Replay. There might be an event coming up that gives you Genesect.
There is not an event to get Keldo YET.
keldo is an event pokemon and you cannot get it in the wild
It has not been announced for any region as of yet. The game has been out for about six months in Japan and they still have not gotten the event, so it will be a while. Please wait patiently.