This year's sub-theme is "RITUALS" Remember, you do not have to use this in your game. Halloween is the main theme, and as long as you have that you're good.
That§s a fairly broad theme and it should be possible to apply it in more original ways than by an inclusion of a cult. It would be nice to make playing the game a ritual. Someone (I am not really capable of that) ought to create a slow game you open every morning during breakfast to check out the progress.