In a Corocoro leak, it has been revealed that Keldeo will, in fact, be the Pokemon distributed to players who pre-order a ticket to the 15th movie this summer.
Tickets are on sale April 14 to July 13.
Players can pick up the Pokemon from June 23 to August 31.
It can be received on Black/White OR Black 2/White 2.
Keldeo will be distributed at level 15.
The advertisement says it'll be good addition to bring in your party at the start of your B2W2 adventure.
And they're hyping that "something will happen" in B2W2 with this Keldeo, but of course no specifics yet.
(all screenshots in this image are from BW)
The official site has revealed this event and more details.
Hold Item: PP Max
Event Gallery entry