Technically, as of now, Kyurem is in the "Limbo" tier, meaning that the majority of the community has absolutely no idea where to put it. The link that Trachy provided is a link to my forum, where we're trying to get opinions to decide where to put him for our tiering of use in PokemonDB.
However, our opinion means nothing to Smogon and other battle communities, so until they release a completely official tier list, we'll have no idea where it's really going. Sorry.
