A ghost game pack like Vampires or Werewolves would be what I want. Ghost should get their own skill tree! Along with a Western ghost town world, where only ghosts live.
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Ghost should have new interactions, gameplay objects and even the ability to possess Sims and make them playable.
A Fortune Teller career could also return, with a local fortune teller Sim living in the world. And a local graveyard lot.