Many MusicBrainz are tied into multimedia franchises. At present the closest thing we have to link all these entities together is folksonomy tags; these are still not supported by all entities and can be messy. What I propose is a new all-encompassing Franchise entity to tie all franchise-related MB entities together.
The main entities that would tie into a Franchise would be Artists, Release Groups, Releases, Recordings, Works and Series (and possibly Events).

I know this will come up eventually, but the main style guideline I'd attach is that the Franchise is not a dumping ground for every piece of media associated with a media franchise. Only franchise aspects tied into music are to be added.