The horror theme that I'd like to see next would be something based on H.P. Lovecraft. I'd probably go with Arkham Horror, which is a fairly popular board game that could likely be lisenced cheaply and provide some direction and artistic assets. The game is set in a fictitious village of Arkham, MA in the 1920s or 1930s. There are various locations on a map: library, bank, train station, town square, asylum, woods, etc. Portals to other worlds, called "gates", are opening in these locations and releasing monsters into our world. Investigators must battle monsters and close these gates. Finally, when enough gates have been opened an "Ancient One" is awoken and the players have to defeat it. Cthulhu is the most famous, but there are many different Ancient One monsters in the game.
I really think that would translate quite well to pinball. I'm thinking a toy similar to the ship on Attack From Mars would work well as the gate. It opens and you must close it, which makes sense with both the toy and theme. I would also use pop targets similar to those on Scared Stiff with smaller monster toys mounted on them. I'm surprised those are not used more as it is free motion, which for me adds interest to the game. Complete a certain number of gates and you start the Ancient One battle(s). Perhaps have a larger toy(s), where the eyes gradually glow brighter, showing that the Ancient One is awakening. Since these are often beasts with tentacles, you could also have the main shots represent each of the tentacles. Cut them off then perhaps back to the gate shot which can also represent the main body of one of the Ancient Ones.
One other unique thing with this board game is that you also are battling your own sanity, which could be cool to try to incorporate into the game. Maybe reverse the flippers or even make it look like there are errors in the the game culminating in it appearing to shut itself off and restart. Perhaps that's more like the ninth reactor in Total Nuclear Annihilation. In saving the world you are sacrificing yourself and enter a state of insanity. It's a fine line between that being confusing versus making the player feel slightly insane in a fun way. Alternatively that would be a fun way to start a midnight madness mode. Basically have midnight madness introduce the fact that you are actually an inmate in the asylum.