This one is spoiler free (obviously as I wouldn't be posting it contained spoilers) as I made sure the keep the tittle to something that does not resemble the real OST name. For the record, I don't really know the full name of the OST anyways. The melody has been seen in an already publicly released song, the main menu theme. It's sort of Kyurem's fanfare theme I suppose much like the main menu theme from Diamond and Pearl was placed in another OST in that game.
Update: Go play the DDR-style game, Thirdstyle, which features this remix!
http://thirdstyle.com/lugiadialga/play