My approach to building horror

This contains some small spoilers for parts of Curse of Strahd. If you are a player in said campaign, you should not read past the "examples from my CoS game" section.

TLDR:

• The GM and the players should agree to build the tension. Horror only works when both parties agree to it.
  
• Use the different aspects of horror. Make it scary, make it creepy, make it disgusting

 

A band of fools fight against the horrors of Barovia

The following post is based on my own experiences with running Curse of Strahd. In addition to the write-up on building horror in the start of the adventure I would also recommend getting your hands on the Heroes of Horror supplement from 3.5e. Although the game mechanics parts of the book is not that relevant for 5e or OSR, the book has some good advice on creating horror.

Scare the characters, not the players

Trying to scare the players is much harder than actually scaring the characters. Most likely you are sitting around a table or playing via Roll20 (or similar websites). This is not exactly ideal for creating a scary atmosphere. Therefore, I propose that the GM should aim for scaring the characters. They are the ones that are actually in the horrifying situations.

This requires cooperation from the players, and a willingness to roleplay. They need to be able to put themselves into the shoes of the characters. Heroes of Horror elaborate on this, and define a “DM/player contract”, which basically states some precautions for both the GM and the player. In short they are:

• Agreeing on where the “line” is, in terms of what the players and GM are comfortable with.
• The GM should make the world dangerous, but make the dangers sparse.
  
• In turn, the players should trust the GM to make things scary, and not use metagame-thinking to ruin the mood.
• The players must accept the horrifying things that are happening to their characters, and play into it.
  
• Players should also aim to create characters that are fitting in a horror campaign. The haunted one background from CoS makes this really easy.
  

Leverage the different aspects of horror

Paraphrasing from the words of Stephen King: If you can’t make it scary, make it creepy. If you can’t make it creepy, make it disgusting. I probably got that wrong somehow, but this is the idea I have used to run Curse of Strahd. Each these types also has different sub-types:

• Scary: resource scarcity, enemy difficulty, hopelessness.
  
• Creepy: a being stalking the players, things changing randomly when someone is not looking, nightmares. 
• Disgusting: body horror, sickness and disease, torture
  

Examples from my CoS game

Bonegrinder (and Berez) can easily be disgusting and creepy. Witches (and especially night hags) is a great way of introducing body horror, sickness, stalking and nightmares. The same goes for the Abbot and his experiments (mongrelfolk and the flesh golem) in Krezk. In my game, the Bonegrinder hags tormented a cleric in his dreams, leading him to going mad and becoming paranoid. In later sessions, I introduced body horror in Bonegrinder. One of the characters has been raised by Morgantha and her daughters, and wanted to seek help from them against Strahd. As a trade, the hags made the character eat an enchanted rat. This turned the character pregnant within ten minutes. She birthed a half-demon baby, which the witches took as payment. In turn they got some strange enchanted berries.

Barovia is packed with difficult encounters which really amp up the feeling of hopelessness and despair. The vampires in the coffin shop in Vallaki is a frequent mention on the CoS sub-reddit. Another encounter that is potentially quite difficult is the Yester Hill encounter with the druids and berserkers. Although some of the druids are busy with summoning Wintersplinter, it is still a pretty deadly encounter. This makes it scary for the characters. They will fear for their lives, and they will feel vulnerable. In my game Wintersplinter had already been unleashed when the players got to Yester Hill. I changed the encounter to serve as a trap created by Strahd. The players has been using Wizards of Wines as a base of operations, and Strahd wanted to end this. Therefore, he summoned Wintersplinter, and had it attack a night the party was resting at the vineyard. One of the characters got killed in this encounter, which lead to the rest of the party wanting revenge. They rushed to the top of the hill, and encountered the druids and berserkers. While they were fighting, Strahd appeared, and pointed towards the vineyard. The players looked back in horror as the vineyard was engulfed in flames. Hopelessness kicked in, in addition to the difficult encounter.

I hope this was somewhat useful.