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- I Cast...Brainstorm issue 37!
I Cast...Brainstorm issue 37!
A weekly newsletter of ideas and advice for D&D Dungeon Masters, players, and fans
Dave Palmer
December 19th, 2025
In partnership with
This week — A Holiday One-Shot Adventure!
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In this issue...
Happy Friday, and Happy Holidays! We’re a Christmas-celebrating family, and I’m really looking forward to a little bit of time off, a little bit of family time, a little bit of creative time, and a little bit of extra D&D time over the next couple weeks!
I’m writing a holiday themed one-shot for the folks in my weekly D&D game, (the ones who aren’t traveling this week), which is something we did last year, too. Read on to see my notes for last year’s one-shot, which is based (kinda sorta) on The Grinch Who Stole Christmas.
Thanks for reading, and may you receive all the RPG gifts your heart desires!
A Holiday One-Shot for Level 5 Characters
I ran this holiday one-shot for my regular in-house group last year, and they seemed to really enjoy it. My notes are below in case you’d like to run it, too! I provided some 4th level pre-generated characters for my game, but five 5th level characters are probably a better power level, since the big bad is a CR 7 Oni. (Of course, adjust the character level and number of characters as needed for your group and game.)
The story leads to the Oni’s cave, and I used a cavern map from another adventure, but if you don’t have something handy, and can’t find anything suitable to download from Reddit or your favorite map maker, then a quick sketch should do to keep things loose and fun. If you get a chance to run Attack on Simril, I’d love to know how your session went, so please reach out and let me know, (and I’m happy to hear any feedback, as well).
Attack on Simril!
I set the story in a small town in the Silver Marches of Faerun, but any remote area near mountains in your game world will work great. To kick things off, read or paraphrase the following:
Adventure Start
It is sundown on Nightal 20 in the Savage North, just south of the Spine of the World Mountains, a wide swath of untamed wilderness wracked with difficult winter weather, and home to many hardy folks and fearsome beasts. Tonight, you and your companions are in the tiny town of Rivermoot to celebrate Simril with your family and friends.
Rivermoot is a very small and isolated hamlet in the Lower Rauvin Vale in the Silver Marches, nestled on the trail between the small town of High Hold and mining city of Nesmé — about two days travel (when the weather is fair) from either place. It sits between the northern bank of the River Rauvin and eastern bank of the River Surbrin, at the foot of the Frost Hills, just south of the Spine of the World.
Rivermoot mostly serves as a way station for miners and merchants traveling either by river or by land — a place for rest, trade, and safety during the harsh winters, when blizzards blow down off the Spine with little warning. Though its small, and on the frontier of the wilder lands to the north, its protected by a sturdy palisade on its east side, and by the two rivers on its south and north-west sides, making it defensible. During spring the rivers often flood, and the majority of buildings in Rivermoot are built standing on pilings at least 10 feet off the ground.
Only a couple hundred people live in Rivermoot year round — merchants, artisans (2 blacksmiths, wheelwright, apothacary, general goods, lion shield coster), innkeepers (there are two inns— one more expensive than the other, but both well managed), hunters, trappers, clerics of a multi-denominational temple (which also acts as a school), a reeve (sherrif) and a few guards, and the families of those folk. And as the sun sets to the west, most of the people of Rivermoot are gathered in the large open field in the center of town.
There, the festivities for Simril are just getting started, and will last until dawn. Simril is the annual winter festival in this part of Faerun, celebrated in the cities and towns up and down the Sword Coast to the west, and in other towns and villages, mostly where immigrants from those cities have settled. When the stars are visible across the sky, celebrants gather with loved ones to cook and eat, sing songs, play games, and gaze at the stars. Its customary to locate stars associated with one’s own birth, or with their ancestors during Simril. Cloudy weather was considered especially favorable, as finding one's star in an overcast sky during the celebration was viewed as a blessing from the goddess Tymora (Lady Luck). Simril is always celebrated outside, with people trying to stay awake the entire night, gathered around bonfires with plenty of music, food, games and warm drinks.
The centerpiece of the celebration, just now being adorned with magical lights created by the local priest of Selune, is a 16’ tall holly tree. The bark is smooth and grayish-brown, and the leaves are dark green with a waxy texture and sharply serrated edges, adorned with bright red berries. The tree has a conical shape, with branches that spread out gracefully from the central trunk, and the twinkling lights nestled in its branches give it a warm and festive air.
The square is full of laughter as the adults prepare, and the children run around throwing snowballs at each other, or dropping to the ground to make snow-devas in the fluffy layer of snow that covers the square. Delphint Farsight, the reeve, (sheriff) of Rivermoot, waves to you from across the field as he helps place one of the long tables around the tree. Some of his guards follow behind, with long benches.
At this point I asked the players to introduce themselves and describe what they’re doing at the moment of the celebration’s start. If they cared to, they could speak with each other, reveal that they traveled to Rivermoor together, and add whatever backstory info they wanted.
Then someone calls for help rolling kegs out from a tavern. Hopefully the characters will go to help, but if not, try to pull them away from the holly tree and distract them with some playful kids, someone asking for help carrying a cauldron to the table, or anything else so they’re not paying attention to the tree when the Oni appears, uproots the holy tree, and carries it off.
If the PCs are helping in the tavern you can read or paraphrase the following, and adjust as needed if characters are elsewhere in Rivermoot when the attack occurs.
You enter the tavern and begins to set two more barrels on their sides to be rolled out to the square. The barrels are heavy, but the good natured townfolk are laughing and bantering as they arrange the barrels in a line aimed at the door.
Suddenly you hear anguished screams, a roar, wood splintering, and a crash!
The characters can act as they wish when they hear the attack. Once they’re within sight of where the holly tree once stood —
You see splashes of bright red sprayed across the snow centered on two dark forms. People are screaming and running away. You hear a loud distance splash coming from the Northwest.
The square is in chaos, with townsfolk crying, running around and yelling for loved ones. Blood spatters the snow, and a large giant sized footprint has created a slippery depression in the frozen ground.
Delphint and two of his guards stand over the dark forms in the snow. One of the guards identifies one form as the body of a guard named Aben and the other as Iyol Mungrim — a young boy. Delphint mutters “Gods be damned” just as Kerim Hallindar, the strong-looking, ruddy faced Priest of Selune who runs the town Temple, approaches at a run. “Don’t say that Delphint! The gods are near this night!”
As Kerim looks over the bodies, Delphint and the guards stalk away to the Northwest. The PCs can decide how they want to be involved. If they go with Delphint, the reeve will pick up the giant’s trail heading into the mountains to the northwest. If they stay with Kerim, the Priest shakes her head and covers the crushed form of Iyol with her cloak. She looks at you and says, “We are in grave danger!”
At some point Kerim should tell the PCs that she was at the edge of the square, when suddenly a 20’ tall creature was standing in the center of the square, appearing from thin air. Aben ran at it and was kicked down, then the creature pulled the holly tree out of the ground and started running away. Poor Iyol, just 14, was in his way, and was crushed by the giant. “But its worse that it appears, I fear…” she says.
“This is the night of Simril, but also the night when Priests of the Auril the Frostmaiden celebrate the Coming Storm. They call on vicious blizzards to torment a town, or even a whole region, though it is said that if, at midnight between the 20th and the 21st, a town displays a holly tree thats deemed worthy of Auril, that place will be protected from her ire. Rivermoot has always featured a beautiful holly tree during Simril, and we’ve always been spared the worst of winter. I fear what will happen if the tree is not returned by midnight!
Please! You must return with the Simril Tree by midnight! Here, take this!” says Kerim, as she hands you a satchel. Inside are 5 potions of Greater Healing, and a scroll tube. “I fear that the giant has fled to the Spine of the world. You must track him and regain the tree, but it could take hours to do so. Inside that case is a scroll of teleportation — read the words upon while while you all touch the tree, and you will be transported right back here to Rivermoot!”
At this point in the story, it should be about an hour from sundown. Anyone in the town can describe the tree, or a check from a character with Nature as a skill could determine that the tree is 16’ tall, with a trunk of 14” at the base, and weights 700 lbs.
Chances are the PCs will take up the quest to recover the tree, and if so, Kerim hands them Potions of Greater Healing, or anything else that you think the characters would need. She also tells the PCs that they won’t survive in the bitter cold of the north if they don’t have cold weather gear, (the townsfolk will gladly supply it and any other gear). Folks from Rivermoot hitch up dogsleds for the PCs — 2 people to a sled and each pulled by 2 dogs (use wolf stats for sled dogs). The PCs are handed bottles of fire brandy (to help keep them warm), extra gear, snowshoes etc. and then they can take off.
As the PCs leave to the northwest, they can see people kneeling and crying over both Aben and Iyol’s bodies.
The wide dock extends half way across the River Surbrin is still intact, as are the ropes and pullies used to pull the dock to the far side of the river. With all of them working together, the PCs can be across in a few minutes, and then they have to track the Oni to its lair. The distance 16 miles west northwest to the southern tip of the spur of mountains where the Oni lives, and the path gets snowier and more difficult to move as the PCs near the mountains.
Searching for signs of the giant’s trail on the way to its lair require appropriate Survival, Perception or other skills. Moving at a fast pace the PCs can move 3 miles/hr for 4 hours, then the dogs must rest 1 hour. Without rest the dogs slow to 1 mile/hr.
However you want to challenge the players, they should be able to each the Spine of the World, (or any mountain range the Oni’s cave is hidden in), around 10:00 pm. A miners’ way-camp is nestled at the base of the mountain, with places to tie off the sleds, and sturdy cabins large enough for the sled dogs, (with water and provisions for the animals). Past the camp, the characters will have to don snowshoes and move on foot. For an extra challenge, maybe there’s a blizzard, too! (Rime of the Frostmaiden has fun rules for blizzards.)
As they search for the Oni’s lair, I had the players choose a navigator to make Survival checks to stay on the Oni’s trail. Any failures meant a roll of a d8 on this list —
Avalanche!
(You can use the avalanche Rules from Rime of the Frostmaiden.)Dead end (lose 15 minutes back-tracking)
Encounter 3d4 Ice Mephits CR 1/2
Encounter an Ice Elemental CR 5
Encounter 1d4+2 Rime Worms CR 1
Encounter 2 Yeti CR 3
Dead end (lose 30 minutes back-tracking)
A White Dragon passes overhead, affecting the PCs with Dragon Fear!
Eventually the PCs will find the lair of the Oni known as The Grinich!
The Grinich’s Lair
The Door
Set into the side of the mountain, creating a 10x10 vestibule, is a huge stone door, inexpertly carved with some sort of writing which has been chipped out of the stone by some giant blade.
Written in Giant runes on the door is “Say nothing and enter”. Anyone making a successful Perception check (you pick the DC) notices that an area high and to the right on the door is worn — if a PC places a hand there, and is silent for 1 second, the door glows, and swings open.
If anyone says anything, even at a whisper, while standing in front of the door, a trap door above opens, and drops boulders into the vestibule. DC 16 Dex save to leap out of the way — 2d10 bludgeoning damage or half on a successful save. The trap door resets immediately after and reloads with more boulders The trap door can be wedged shut by a rogue with a successful Thieves Tools check.
The cave entrance
The stone door opens into a natural cave that extends into the mountain. In the distance the PCs can see a faint light.
If the PCs aren’t moving stealthily, small crystals spread on the floor of this tunnel will crack and pop as the walk forward (alerting the Oni and the wolves).
A tunnel
The tunnel from the south drops a few feet into this roughly 20x20’ chamber. High steps up to the NE and SW lead to other chambers. From the NE, you detect a faint light.
A crossroads
There is an awful smell coming from the west, where some crudely arranged stones work as a set of steps leading down about 5’.
The trash heap
This room smells horrible, and is full of waste, offal, broken crates and other trash.
If the PCs decide to dig through the trash, roll a d20 —
1-10 — They find nothing
11-14 — Something disgusting splashes up and gets in the PCs mouth.
CON save DC 15 or contract a disease!
15-18 — The PC injures themself on a rusty nail or a broken rib bone— 1d4 piercing damage
19-20 — They find treasure!
Huge Cavern
You enter a huge cavern from the south, which is much warmer than the rest of the cavern. It is faintly lit by lantern suspended from a pole that rises 25’ into the air. The pole also extends down into the ice as far as you can see (only about 5’), and is next to another large structure that is also set into the ice. Blood is pooled on the floor in front of the structure, and hanging on it by ropes are disemboweled and dressed corpses — an elk, a small humanoid (a dwarf), and a yeti.
Four more passages lead off to the NW, N, E and SE. From the NW passage, you distinctly hear growling.
The structure is an ancient and gargantuan sculpture. Grinich the Oni doesn’t know anything about it, except that he likes it, and its useful for hanging meat. Grinihch is on top of the structure, invisible (or someplace else, hiding until he attacks!)
Wolf Den
This cavern smells of animals and blood. The floor is covered with dirty fabric, and strewn with bones.
Grinich’s two Winter Wolves sleep here. They attack intruders on sight. Once engaged, Grinich will help them!
Mining Gear Cavern
At the far end of this cavern is some mining gear, marked with the sigil of one of the local dwarven mining companies.
The gear has obviously recently been used to chip crystals off the back wall of this room. Grinich is expanding his lair, and uses the crystals as a warning system in Room 2.
Mephit Room
This room smells of rotten eggs, and is extremely warm. Its hard to see clearly, as steam rises from three round natural vents of bubbling water.
If the PCs disturb the vents, Steam mephits attack. The mephits will not leave the room.
Pool of Water
Half of this room is filled with a pool of clear, sparkling water. The water is cold and perfectly fine to drink.
Shrine
Rivermoot’s Holly Tree has been set in front of a wide shrine, from the crude carvings its clear that it is dedicated to Auril. Crates and barrels are stacked to either side of this room, with glinting treasure visible in some of them.
At the DM’s discretion, one of the stacks of kegs can be a Keg Golem that fights with the Oni.
The Oni is angry that smaller creatures would dare to enter its lair, and it will become even more enraged if they dare touch the Holly Tree that it took as a gift to Auril.
Also, the Oni known as the Grinich hates loud sounds, and as it fights it will say “Noise! Noise! Noise!” as it swings it massive glaive +1.
Epilogue
Once the holly tree has been secured, the PCs can use Kerim’s gift to return to Rivermoot, and the celebration can continue!
However if the Grinich isn’t slain, it will return to the town the following year.
If the Grinich (and its allies) are slain, the PCs can have their pick of whatever amazing treasures the Grinich has stowed around his lair.
Brainstorming Links
You probably already know about the folks below, who are real inspirations to me, but if not, do yourself a favor and check them out.
The Arcane Library — masterpiece adventures, and Shadowdark, too!
https://www.thearcanelibrary.com
The Angry DM — so angry….so many great ideas….
https://theangrygm.com/
DMDave — on point analysis of D&D rules, and a ton of fun ideas
https://bsky.app/profile/dmdave.bsky.social
RPGBot — whip smart critique and explanations of 5e rules
https://rpgbot.net/
Sly Flourish — a DM’s best friend who is also a better DM
https://www.slyflourish.com/
Treantmonk — years of helpful advice and clever ideas
https://www.youtube.com/@TreantmonksTemple
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