Check out this new article Wizards of the Coast posted recently:
Far Realm Fiends
The Far Realm is one of the last unexplored regions of the multiverse—a place beyond reality. Few mortals dare glimpse it and fewer still travel there. To help you flesh out a campaign that takes characters into the Far Realm, this article presents several creatures and hazards, as well as advice and ideas for how to make the Far Realm your own.