The Cthulhu Mythos, a creation of HP Lovecraft, has become an enduring and beloved source of cosmic horror that continues to fascinate fans of horror in various media, including D&D. Its themes of investigation, terror, and the unknown have inspired countless stories and campaigns that evoke the spine-chilling terror of the ancient and malevolent beings that inhabit Lovecraft’s fictional universe. In this article, we’ll explore ways to incorporate the iconic themes and creatures of the Cthulhu Mythos into your D&D campaigns to create a thrilling and immersive horror experience for your players.

Witness the unexplainable

One of the core features of Cthulhu Mythos is the horrors that are not easy for the mind to comprehend. When it comes to D&D however, you might find it hard to come up with something unexplainable. After all, there are many realms in this system with all the creatures defined properly, and libraries of books of wizards and other loremasters, right? 

Well, there are still things that you can find in D&D that lurk beyond the known cosmos, coming from realms far away. Aberrations of very alien nature can come to your realm to inspect the lowly habitants there, or perhaps to outright invade or dominate them. As many aberrations have features that are very horrific, you can easily find or create some of these monsters to have the horror of the unexplainable on your table.

Power of Suspense

Most of us may be used to the regular drill of D&D where we take quests, discover the locations or targets, and then bash the threat with our greataxe. Encounters of combat often take up most of the time in our games. However, in a story of investigative nature, you might want to slow things up a bit. Sure, the PCs can still shake the coven of cultists here, or eliminate a bunch of minions there, but the sense of mystery must persist for the proper taste of an investigation.

In such a setting, try not to provide all the information in one location. The PCs may need to find pieces of the puzzles in various places they go, and then put the pieces together in order to understand what is going on. In addition to this, a good plot twist at the end where a character the PCs don’t expect turns out to be the villain or the butler of the horrific entity can be the cherry on top.  

The Unkillable

In D&D, everything has a challenge rating, and everything can die if you hack and slash them to zero hit points. Yet, an essential of the cosmic horror is to have a threat that cannot be eliminated. A monster or villain that the PCs need not to fight but to run away, or hide, is the key here. Such a creature may need to be weakened by a specific ritual or an artifact in order to be challenged by the PCs. Until then, they should try to avoid its wrath, or be perished by its -unfairly challenging in terms of CR- abilities. It is also useful to use such a monster as the scare element of the game, where it pops up here and there and causes the PCs to experience hard escapes and thrilling chases.

Some Rules for Lovecraftian Investigation

We have also come up with two experimental rules for Lovecraftian horror and investigation for your 5E games. They can bring a new flavor to your games, have a look!

New Rule for Cthulhu Mythos: Sanity

Sanity is a big part of Lovecraftian cosmic horror. The despicable and unexplainable nature of these horrific monsters does not make it easy for one’s mind. On top of that, the fundamental nature of these cosmic entities are often too complex for one’s mind to safely comprehend. Here is a simple Sanity system that you can use in such a game style: