For adventurers who regularly face terrifying monsters, it's easy for familiarity to sap the frightfulness from terrible foes. Restoring mystery and menace to even the most ordinary monsters can be a simple matter, though, and enhances the atmosphere of horror adventures. Six simple techniques can transform a pre-existing stat block into a horror to haunt the characters' dreams:
Monstrous Origins. Monsters in Ravenloft can be every bit as unique as player characters.
Notorious Monsters. A monster is more frightening when its reputation precedes it.
Describing Monsters. Dwell on a monster's description to really build tension.
Monstrous Tactics. Monsters that fight dirty—or in a particularly fearsome way—have more impact.
Monstrous Traits. Simple tweaks to a monster's stat block can enhance its horror.
Monstrous Minions. Simple traits can reflect a monster's relationship to the evil master it serves.
Examples are provided in each of these sections, though make sure to come up with original ideas to use as well.
A variety of explanations, from transformative curses to magical experiments, can justify the appearance of a unique individual with unusual traits. In the same way, monsters in Ravenloft don't need to be members of a species or society. There can be a vicious @Merrow living under a bridge or a @Yuan-ti Abomination Darklord without having to explain @Merrows as a species or the nature of all yuan-ti in the setting. Monsters can be one-off flukes of nature or the products of insidious magic.
For significant adversaries, use the tables in the lore articles found under the Genres of Horror folder for inspiration as the DM crafts a monster's unique details. When it comes time for the final confrontation, it might not matter whether the bridge-haunting @Merrow was the product of an amoral experiment to infuse piscine traits into a soldier or the result of someone drinking from a spring tainted by demon's blood; the @Merrow's stat block remains the same. But those different origin stories suggest completely different paths for adventurers to follow when investigating the creature and ensuring nothing like it ever returns to be a menace again.
Every monster tells a story. The more monsters are treated as unique individuals and have their threats foreshadowed, the larger they'll loom in characters' minds. Build dread by giving monsters reputations that suggests their form, deeds, or peculiarities while letting players' imaginations embellish details.
For example, tales describe a horrifying skeletal figure that corrupts the land wherever it walks. Its habit of whistling cheerfully while committing brutal acts is the source of its epithet: the Whistling Fiend. Characters might hear rumors of its merry tunes becoming fearful earworms for those who survive its passing. A party seeking the monster might also hear the whistling long before they confront the fiend. All that time, they can at guess at their enemy's nature, but ultimately the Whistling Fiend might be any demon or other threat of the DM's choosing.
The Whistling Fiend's notoriety has little to do with its stat block. It's famous because of its habit of whistling amid acts of terrible carnage. Come up with original traits and characteristics like this to add flair, flourish, and fright to color a monster's notorious reputation.
When adventurers encounter a monster for the first time, especially if its reputation precedes it, dwell on its description. Tell the players that they see a @Merrow or describe the appearance. But that first moment of revelation is the best time to paint a horrifying picture of the monster in the players' imaginations. In addition to the techniques described in the Horror Pacing & Gameplay, and Describing Horror lore articles, consider these concepts when describing a monster:
Emphasize Wrongness. Focus on the features that make the creature alien, inhuman, and out of place. For example, the Whistling Fiend looks like a humanoid skeleton dripping its own gelatinous musculature. Its skull curves to a point suggestive of a sickle.
Engage All the Senses. Describe elements of the creature that are likely to provoke a visceral response, such as the smell of rot that its oily flesh exudes, the whistled tune of a well-known nursery rhyme issuing from its lipless mouth, and the unnatural heat that forms ripples in the air around it. These details don't need to rely on grotesque descriptions. Sometimes it's a contrast between mundane and terrifying details that stands out, like a monster's soulful eyes or pearly teeth set amid vicious features.
Make it Personal. There's a fine line here: Don't dictate a character's actions in response to what they see. But do touch on the feelings that the creature provokes, leaving it up to the players to describe how they respond to those feelings. Their gut twists in revulsion. The acrid air stings their nostrils. They're suddenly aware of how small and hollow their dreams are in a world that can spawn beings of pure evil.
Monsters, just like player characters, can try anything that can be imagined in combat, including the full range of combat options outside of their stat blocks. Monsters can use the Help action to aid each other, they can grapple or shove their enemies, and so on. Some monsters use these options to maximize their advantages in battle; others use them to sow fear among their enemies, even if they're not strategically optimal choices.
For example, creatures known as "goblyns" in Kartakass and other domains are ordinary @Hobgoblins in terms of their game statistics, but they're known for a tactic they call "feasting": they grapple their enemies and then make unarmed attacks to bite their faces. These attacks aren't terribly dangerous (a @Hobgoblin's unarmed strike deals only 2 damage, compared to the average of 5 it deals with a longsword), but the face-biting is much more shocking to the victim and onlookers.
Monsters become more fearsome if they use tactics like ganging up on the least-armored characters in a party, taking the time to take bites from unconscious foes, separating party members from each other, and attacking from hiding. Use these tactics judiciously; the goal is to surprise and scare the players, not to convince them that they're being set up to fail.
Consider undermining players' expectations about what a creature is or can do by making tweaks to the traits in its stat block. Adding a @Sahuagin's Blood Frenzy trait to a different monster can help it feel like a bloodthirsty horror, for example. Traits such as a @Troglodyte's Chameleon Skin or a @Doppelganger's Ambusher can help make a monster feel more sinister as it lurks in hiding and ambushes its foes. Some traits, such as a @Night Hag's Etherealness or an @Imp's Invisibility, can help a monster escape from an encounter so it can return to haunt the adventurers another day. Traits such as a @Banshee's Horrifying Visage or an @Adult Black Dragon's Frightful Presence can heighten the inherent fearsomeness of truly terrifying creatures.
Of course, do not be limited to the traits that appear in existing monster stat blocks, but those are a good starting point. Feel free to be inventive and come up with original ideas.
In the Land of @The Mists, many monsters serve as minions or manifestations of more powerful villains. To reflect a minion's relationship to its Darklord master or other sinister forces, add one or more of these traits to a monster's stat block.
Alien Mind. If a creature tries to read the minion's thoughts, that creature must succeed on a Intelligence saving throw with a DC equal to 10 + the minion's Intelligence modifier or be stunned for 1 minute. The stunned creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
Minion's Mind. The minion can't be compelled to act in a way contrary to its master's instructions.
Sacrificial Minion. When the minion dies, its master regains hit points equal to four times the minion's challenge rating, as long as the master is within 100 feet of it.
Selfless Bodyguard. When an attack hits its master and the minion is within 5 feet of its master, the minion can use its reaction to make the attack hit itself instead.
Telepathic Minion. The minion and its master can communicate telepathically with each other, as long as they are on the same plane of existence.
Once the techniques in this article have been considered, put them all together to create a truly unique terror. If there are any ideas about what the DM wants their monsters to do, keep them in mind. Then think of what stories connect the pieces they want to use or fill in gaps they don't know about yet.
For example, perhaps there's an idea for a @Troll that ambushes adventurers while they rest. Considering its origins and appearance, the troll literally being a @Troll isn't important; it's the general challenge and look for the creature that's more interesting. To make the troll feel notorious, think of what would scare adventurers—where they're vulnerable and what they're sensitive about. There is an idea for a creature that can come from anywhere, maybe even within the adventurers' own gear. With tactics and traits in mind, think of the troll as an abductor and give it the Grappler trait of a @Mimic and the Amorphous trait of a @Black Pudding so it can sneak in anywhere. Finally, don't think of the troll as a minion, but give it the Alien Mind trait to reflect its tormented psyche. Then flesh out its story and give it a name: @The Bagman.
The above paragraph was merely an example, make sure to come up with original ideas and do not simply copy this one.