Ghost and haunting scripts want breath and space: the Whisper delivery, the Ghost effect and plenty of pauses. Demon voices want weight: a gravelly voice such as Algenib, the Slower delivery, the Monster effect and a <growl> at the start. Both suit haunted houses, horror games and spooky short videos.
Analog horror, the found-footage style built on eerie emergency broadcasts and old training tapes, works best with almost no emotion. Use a calm, informative voice such as Charon or Kore, the Calm delivery and the Radio effect, which narrows the sound to a 300 to 3,400 Hz band with a little hiss, like an old broadcast. To change your own recording instead, try the ghost voice changer or the monster voice changer. For a booming, dramatic read rather than a whisper, the movie trailer voice generator is the better fit.