This week’s encounter is The Dying Unicorn, a high-stakes puzzle encounter that may become a lethal combat if the characters fail to solve the puzzle in time. Speaking as both a designer and a Dungeon Master, I enjoy giving puzzles surmountable failure states. In video games like The Legend of Zelda, it’s okay to refuse to allow the player to advance through the dungeon until they complete a mandatory puzzle. That’s not acceptable in a game like D&D. Puzzles in tabletop RPGs need failure states beyond “You take 2d6 damage and the puzzle resets. Try again.”

In this encounter, failing to solve the puzzle in time results in a double crisis: an NPC begging for their help is killed by evil magic, and then that same evil magic resurrects the NPC as a monster, forcing the characters being into a deadly combat encounter. I hope this ready-made encounter does more than provide you an hour or two of entertainment—hopefully it will inspire you to make even better puzzle encounters!

Puzzle Encounter: The Dying Unicorn

This puzzle encounter may result in a combat encounter balanced for a party of 2nd-level characters, but can be scaled up to challenge a higher-level party.

A holy pool rests in the midst of an emerald-green forest. Every day, at dawn, a golden-horned unicorn drinks deeply from the pool’s glassy waters, then gambols through the forest. The unicorn is named Ehlonna-Vassorum, for he is the dutiful vassal of the goddess of nature known to humankind as Ehlonna. The forest and all its creatures are his charge, and he deals swift justice to those who fell the forest’s trees and slaughter its children.

This creature is a thorn in the side of people who long to exploit Vassorum’s Wood for their own ends. Their identities are not important—perhaps a necromancer hired by a local town’s lumber baron, a shadowy sorcerer who seeks to enhance her powers by linking the pool to the Shadowfell, or a mighty devil who wishes to corrupt Ehlonna’s sacred wellspring and transform it into a portal to Avernus. This villain has poisoned Ehlonna’s spring with blasphemous magic, and the unicorn Ehlonna-Vassorum unwittingly drank from its tainted waters.

The unicorn now lays upon its side, powerless and slowly dying, by the waters of the pool. All he needs to restore its magical powers and cleanse itself of this corruption is to drink the purified waters of his goddess’s pool once more, but he lacks the power to restore the pool in his weakened state. The player characters stumble upon Vassorum while wandering through the woods—perhaps seeking Vassorum’s aid on some other quest.

Encounter Summary

The forest known as Vassorum’s Wood is said to be protected by a unicorn with a gleaming golden horn. The wood is named for him, and he is a servant of the nature goddess Ehlonna. While wandering through this forest, the characters find a dying unicorn near a polluted pool. The unicorn tells them of a ritual that can be performed with holy water vessels to purify the water, but it is too injured to conduct the ritual. If the characters are able to solve the puzzle required to complete the ritual in time, the spring is purified and the unicorn can drink from it. If not, the unicorn perishes and transforms into a monster, which immediately attacks the characters.

Encounter Start

When the characters arrive at the polluted pool, read or paraphrase the following:

You brush aside a branch and enter a wide clearing with a pool in its center. The pool looks like it may have once contained water, but is now filled with an oily black liquid covered with violet iridescence. At the edge of the pool is the body of a horse with a golden mane and a dirt-caked white hide.

The fallen horse is the unicorn named Ehlonna-Vassorum. If a creature approaches him, he weakly turns his head to look at the creature, revealing that the creature’s golden horn has turned almost pitch black. It telepathically says:

“Please… I am dying. I need your help.”

If asked to explain the situation, the unicorn knows the following information:

The spring was defiled with dark magic by one of the forest’s enemies.

He drank from the spring before the corruption became visible, and is now being eaten from the inside out by the evil magic.

The dark magic has severed his connection to Ehlonna and thus sealed his magic. If the spring is cleansed, its water can undo the corruption.

Ehlonna left her ancient followers a ritual to cleanse the spring in case it was ever corrupted. Unfortunately, those followers have long since died out, and only creatures with hands can perform the ritual. The unicorn looks forlornly at his hooves as he says so, then gestures to the spring.

After the unicorn gestures, read or paraphrase the following:

Your eyes follow the unicorn’s gesture, and you see a small island in the center of the pool. A statue of a beautiful, fat woman with flowing hair and wearing a gauzy robe stands in an island in the middle of the spring. Three ornate jars are arrayed at her feet.

The unicorn says one last thing:

“My eyes grow cloudy… I sense I have only minutes before the shadow claims me. The statue of my lady Ehlonna… she bears a tablet with… the instructions.”

The unicorn then falls into a catatonic slumber. Nothing short of drinking the sacred water (and being cured of his poison) will save him. The curse that is killing him is too powerful to be broken by remove curse; its power is directly linked to a plane such as the Shadowfell or the Nine Hells, and cannot be broken by any spell except wish.

Puzzle: Purifying the Corrupted Spring

The corrupted spring is a circular pool of water with a 20-foot radius. The island in the center is a small mound of earth with a 10-foot radius. (Thus, only a character who can jump 10 feet can jump from the edge of the pool to the island without touching the water.) The pool is only 3 feet deep.

A creature that begins its turn in the corrupted water or touches it for the first time on its turn takes 3 (1d6) necrotic damage.

At Higher Levels: If the characters are at least 5th level, increase the damage to 7 (2d6). If the characters are at least 11th level, increase the damage to 21 (6d6). If the characters are at least 17th level, increase the damage to 63 (18d6).

On the island is a statue of the goddess Ehlonna, holding three stone tablets in her hands. Upon the tablets are written the following:

My sacred spring is a gift unto you, my faithful. Should evil ever profane it, I gift unto you the method to restore it. Recall the fable of the eight archdruids. Once upon a time, eight mighty druids resided within this forest within three houses. Five were woman, three were men, and together they made eight. In the end, all eight found love in pairs. Four of the druids settled within one house, four settled within another, and the third house was left empty and was reclaimed by the forest. At my feet rest three blessed vessels. Fill them with the profaned water in the manner of the eight druids, and speak my name with hope in your heart.

The three jugs are made of simple clay, but have somehow withstood the centuries. On the face of one is marked VIII, on the face of another is marked V, and on the face of the third is marked III. They seem to be of inconsistent size and weight, and have no measurement markings. These pristine vessels are gifts from the goddess Ehlonna, and cannot be marked or blemished in any way. If a character uses their action to try to physically or magically mark the jug, that character must succeed on a DC 13 Constitution saving throw or take 3 (1d6) poison damage.

At Higher Levels: If the characters are at least 5th level, increase the damage to 7 (2d6). If the characters are at least 11th level, increase the damage to 21 (6d6). If the characters are at least 17th level, increase the damage to 63 (18d6).

Puzzle Solution. The solution to this puzzle is somewhat obscured by the fable of the archdruids. One jug can hold 3 gallons of water, one can hold 5 gallons of water, and one can hold 8 gallons of water. In order to solve the puzzle, one jug must contain 4 gallons of water, another jug must contain 4 gallons of water, and the other must be empty.

The characters must fill the 8-gallon jug to the brim from the pool, and use the other two jugs to divide the water until 4 gallons of water are in the 8-gallon jug, 4 gallons are in the 5-gallon jug, and 0 gallons are in the 3-gallon jug. This solution must be reached before the unicorn dies. The quickest solution takes eight steps:

Fill the 8-gallon jug to the brim from the pool. [8, 0, 0] From that jug, fill the 5-gallon jug. [3, 5, 0] From that jug, fill the 3-gallon jug. [3, 2, 3] Pour the filled 3-gallon jug into the 8-gallon jug. [6, 2, 0] Pour the contents of the 5-gallon jug into the empty 3-gallon jug. [6, 0, 2] Fill the 5-gallon jug from the 8-gallon jug. [1, 5, 2] Fill the 3-gallon jug from the 5-gallon jug. [1, 4, 3] Empty the 3-gallon jug into the 8-gallon jug. [4, 4, 0]

Time Limit. The unicorn has 2 minutes to live from the moment the characters read the stone tablets. (Since D&D rounds are six seconds long, you can track minutes in rounds by using a d10 to count up from 0.) Filling a jug from the pool, emptying a jug into the pool, or pouring water from one jug to another takes an action. Only one character can interact with a jug per round.

Success. If the characters solve the puzzle and speak Ehlonna’s name aloud, completing the ritual, all three jugs flash with emerald light, and tendrils of energy extend from the jugs into the pool. The water shines with green light, then fades to a pristine, almost mirror-like surface. A gurgling of water can be heard as the empty jug fills to the brim with purified sacred water. Dribbling this water into the unicorn’s mouth awakens him.

See the Ehlonna’s Vassal section at the end of this encounter.

Combat Encounter: The Fallen Unicorn

If the characters do not solve the puzzle within 2 minutes’ time, the unicorn makes a loud choking noise. Read or paraphrase the following:

You turn and see the unicorn’s horn turn completely black, his lustrous white coat turn dull and dun, and his golden mane fade to ashen gray. His chest stops rising. A dismal silence settles over the glade. Then, a dull rumbling echoes around you. The trees seem to close in, and the light filtering in through the canopy dims.

Then the unicorn stands. Its horn has crumbled to dust, and a ghastly mist surrounds its body. It gazes upon you with glowing red eyes—then its entire body flares with crimson light as its mane and tail erupt into roaring flames.

The corrupted unicorn has become a nightmare.

At Higher Levels: If the characters are 5th level or higher, the nightmare’s hit points increase to 136. Also, if the characters are at least 11th level, read or paraphrase the following:

Then, the pool explodes. A column of corrupted water sprays into the air, showering everyone with foul drops and smashing the blessed vessels upon the ground. An ominous, humanoid silhouette pulls itself, inch-by-inch, from the statue of Ehlonna. The form of a towering, seven-foot-tall warrior with pallid gray skin and spiked plate armor steps forth and ignites a lance of hellfire in its hand. It turns to you with a smirk. “This sacred wood will fuel the fires of my master’s forges. Flee or suffer.”

This devil is a narzugon, the damned soul of a paladin who forged a pact with a devil. If the characters are 17th level or higher, a second narzugon emerges from the statue immediately after the first. If you do not have Mordenkainen’s Tome of Foes, you can use an erinyes instead of a narzugon, but give her a shield, improving her AC to 20.

All creatures in the glade, except for the nightmare and the narzugon, must make a DC 17 Constitution saving throw as corrupted water rains down upon them, taking 42 (12d6) necrotic damage on a failed save or half as much on a successful one. If the characters are at least 17th level, increase the save DC to 19 and the damage to 84 (24d6).

Ehlonna’s Vassal

If the characters saved the unicorn, he stands tall and proud as strength returns to his body. The inky-black shell around his horn begins to crack and streams of golden light shine through, until the darkness is dispelled with a loud CRACK and entire horn glows with light. The unicorn bows his head to you and says, “My name is Ehlonna-Vassorum, guardian of this wood. I am in your debt.”

If the characters did not save the unicorn, but defeated the corrupted unicorn (and any other evil creatures), a silvery apparition of the unicorn appears at the base of the statue of Ehlonna. His voice rings out telepathically, saying, “This spring is no longer safe. Take a cupful of its water—protect it. Find a new spring in a new forest, and let Ehlonna’s light guide you.”

Your Reward

If the characters saved the unicorn, he bows before the characters and vows to travel with them and protect them for 1 full month, before returning to this spring. If this seems like too powerful a boon for 2nd-level characters, the unicorn may offer his aid with one condition: he is a pacifist and refuses to attack or kill any living creatures, except for fiends and undead. If the characters did not save the unicorn, a quiver of Ehlonna appears in the arms of the statue.

At Higher Levels: If the characters are at least 5th level, all arrows stored within the quiver become +1 arrows for 1 minute after they are removed from the quiver. This bonus increases to +2 if the characters were at least 11th level when they received the quiver, or to +3 if they were at least 17th level.

Did you like this adventure? You can pick up more adventures I've written on the DMs Guild, such as The Temple of Shattered Minds, a suspenseful eldritch mystery with a mind flayer villain (for 3rd level characters). My most recent adventure is in Dragon Heist: Forgotten Tales, a book by the Guild Adepts which gives you a new beginning, middle, and end to Waterdeep: Dragon Heist. It's the perfect way to give this adventure even more replay value! My new beginning is a great way to introduce a campaign focused on either the drow or devil cult factions causing trouble in Waterdeep.

If you want Adventurers League-legal adventures, take a look at The Cannith Code, set in the magic-punk Eberron campaign setting, All Eyes on Chult, a high-stakes adventure set in Port Nyanzaru included in Xanathar's Lost Notes, or Fire, Ash, and Ruin, a demon-filled dungeon delve in an active Chultan volcano! This post contains DMs Guild affiliate links, which means that I—James Haeck—get an extra 5% of the sale if you buy anything from the DMs Guild using these links. You don't pay any extra, but your purchase helps support my work. Thank you so much!

Also, for more free encounters, take a look at the other encounters in the Encounter of the Week series!

James Haeck is the lead writer for D&D Beyond, the co-author of Waterdeep: Dragon Heist and the Critical Role Tal'Dorei Campaign Setting, the DM of Worlds Apart, and a freelance writer for Wizards of the Coast, the D&D Adventurers League, and Kobold Press. He lives in Seattle, Washington with his partner Hannah and their feline adventurers Mei and Marzipan. You can usually find him wasting time on Twitter at @jamesjhaeck.