It's what every Dungeon Master fears. You've set up an elaborate encounter, led the players right into a trap, they've rolled initiative, and yet once your monster shows themselves, the players just don't get those chills down their spine like you were hoping.

If you’ve ever run into this situation, this article is for you! We’re going to share some examples of classic Dungeons & Dragons monsters that will strike terror into the hearts of your players, simply by stealing a feature from another creature—or, as we like to call it, by doing a monster mash!

• Gelatinous cube + roper
• Mind flayer + doppelganger
• Carrionette + nothic
• Zombie + wolf
• Mimic + elder brain

Let's Upgrade These D&D Monsters!

Gelatinous Cube + Roper

One of the most recognizable monsters in D&D, the gelatinous cube is a slow-moving sludge box that can already be an intimidating foe, especially to lower-level parties.

However, their relatively low AC, slow movement, and lack of a ranged attack mean that seasoned adventurers might not find them nearly as intimidating. But what if suddenly a gelatinous cube wasn't content to slide across to its prey? What if, as your players maintained a "safe" distance while mounting their ranged attacks, suddenly the monster lashed out with an oozy tentacle, snatched a character, and pulled them into its acidic body?

This can be achieved with the simple addition of the "Tendril" and "Reel" abilities you'd typically find on a roper. Suddenly this slow-moving, sentient acid pit has become an active predator, a demented ooze fisherman ready to snatch your players' characters up and slowly devour them. 

Mind Flayer + Doppelganger

The mind flayer is one of the more frightening adversaries you can face in a D&D campaign. They combine the sophisticated predatory threat of a vampire, the aberrant otherworldly terrors of the Far Realm, and the obsessive hunger for brains of a zombie. Whether they're a scrounging remnant in the Underdark or commanding whole realms of subjugated beings, when an adventurer faces off against a mind flayer, it should be a terrifying experience.

Imagine then, if your players come across a mind flayer while traversing underground caverns and don't immediately know it. Absent are the usual tentacles protruding from its face or the glaze of mucus across its mauve skin. Instead, the mind flayer takes on the form of someone the characters know. Someone they trust. Perhaps someone they care about, or even someone else in the party.

With the simple addition of the doppelganger's Shapechanger ability, and utilizing the mind flayer's ability to cast detect thoughts at will, you can transform what's already a potentially terrifying encounter into the psychological horror of the "stranger among us" trope. Your players suddenly may find themselves trying to determine who the impostor is, with failure coming at the cost of their brains. 

Carrionette + Nothic

You know the classic horror trope where a character has an evil clone, and their friends can't tell who is the good one and who is the bad one? After a scuffle between the two identical rivals, the friends will say something along the lines of, "To prove to us who the real Johnny is, tell us a fact that only he would know!"

Well, carrionettes aren't exactly evil clones, but thanks to their Soul Swap ability, they can easily engineer a situation where you're not sure if a character is actually in control of their body. Their main weakness when using their body-inhabiting powers is that they don't retain the knowledge of the body's previous occupant. But, there's a way we can get around this issue.

With the help of the nothic's Weird Insight, your carrionette can learn some of its victim's deepest and darkest secrets before it uses its Soul Swap to steal their body. Then, when the player whose body was stolen resurfaces, the carrionette will be able to  turn the unwitting party against their own ally. Using this power, your living dolls could infiltrate every aspect of the party's lives, and they wouldn't even know until it was too late.

Zombie + Wolf

Zombies in D&D don't always have the same impact as the zombies we've come to know and love in other media. These mindless minions are great for imbuing a little bit of grim flavor into a dungeon crawl or as part of a necromancer's entourage, but when was the last time your players truly felt threatened by the walking dead?

Well, one of the scariest aspects of zombies in horror films is their danger in numbers. While a single shambling dead guy might not seem all that intimidating, the threat level increases exponentially the more walkers you have around. Enter the Pack Tactics ability. This little feature, customarily saved for hunter-type beasts, like hell hounds or wolves, is a pretty simple addition, but it produces terrifying results. The ability to attack with advantage when another zombie is within 5 feet of their target means that even your highest AC party members will be taking hits.

Speaking of bringing back classic zombie stereotypes to the detriment of your party, whatever happened to transforming into a zombie if you get bitten? Well, you can make sure your party will be booking it to the nearest temple if you give your undead the choice of a Bite attack similar to the death dog's, in addition to their usual Slam attack. All you have to do with the death dog's ability to achieve the desired effect is adjust it so if the infected creature reaches 0 hit points, they rise as a zombie after a predetermined time.

Mimic + Elder Brain

Finally, we come to a favorite monster of mine and many other nefarious DMs, the mimic. This one might need a little more buy-in from the players, but if they're down for it, it can give them a true psychological horror experience: mash the mimic with an elder brain. This gives the mimic access to two powerful tools, the modify memory spell and the Creature Sense ability. We can then use modify memory for one very specific, very dastardly purpose, to make the characters forget the mimic was ever there. 

Imagine a party of characters making their way through a dungeon, collecting wounds whenever they get close to particular inanimate objects, but never knowing what attacked them or even having a memory of the attack itself, only the wounded aftermath. The players don't initially understand what is happening to their characters, and the mystery of their attackers is the puzzle they need to work out. 

This horrifying experience can be all the more spooky when the mimic uses the Creature Sense ability to automatically know the location of its tortured prey. What tactics would the party have to devise to see and remember the attacks? How would they be able to counter a seemingly omnipotent shapeshifter that can rewrite their thoughts? Suddenly, a single encounter has become an entire creative session concept!

What's Your Favorite Monster Mashup?

Even a minor tweak, a single ability mashed into your monsters, can entirely change the way your players interact with a familiar foe. If you're looking for more ways to spook your party, Van Richten's Guide to Ravenloft offers some great advice. But if you just want to dive into inventing your own mashups, you can start by thumbing through the monster stats in the basic rules and looking for inspiration! 

Riley Silverman (@rileyjsilverman) is a contributing writer to D&D Beyond, Nerdist, and SYFY Wire. She DMs the Theros-set Dice Ex Machina for the Saving Throw Show, and has been a player on the Wizards of the Coast-sponsored The Broken Pact. Riley also played as Braga in the official tabletop adaptation of the Rat Queens comic for HyperRPG, and currently plays as The Doctor on the Doctor Who RPG podcast The Game of Rassilon. She currently lives in Los Angeles.