- People are buying lots of candy.
- People are thinking about horror-themed games.
- Curses are a good place to start. My personal favorites are the Crawler's Curse and the Curse of Crows. Two troublesome maledictions with a horrific theme.
- Taking a psychological approach, the Demon Vial offers a different view on horror, where the possessor must face an assault delivered through dreams and visions.
- The Demon Spawner provides a potent foe with a horrific nature.
- Have a horrible foe lined up and need some props for them? Consider arming them with the Demon Bone Flail or setting them up with the Circlet of Mental Mastery, two magic items with a dark tone suitable for horror.
- Need to make your zombies and ghouls more potent? Consider infecting them with a nice disease or giving them a poisonous touch. My personal favorites from these categories are right here.
- Need a cast? Consider adapting the Jungle Ghoul, Door Haunts, Revenant Spiders, or Mind Eaters to your campaign.
- Finally this adventure arc isn't necessarily straight up horror, but there are certainly horrific elements to the story, particularly the Horrid Minions that appear in the adventure.
(and don't forget the Milky Ways)