From the announcement:
We didn't make it to June 1! Smash Up's next expansion was already spoiled, so here it is to make it official. The next Smash Up expansion will be "The Obligatory Cthulhu Set." The international gaming authority informed us that by law if a game goes more than 2 expansions you must include Cthulhu in some way. This set features crazy Cthulhu cultists, fishy Innsmouth locals, horrifying Elder Things, and good old Miskatonic University members (the Fightin’ Cephalopods). To be certain we got it right, this set also includes a new card type fittingly known as “Madness”, that each of these groups use to various effects. But remember that Madness brings you power but at a price.
We'll have the official product page for it up next week with the first previews!