Example Puzzle Dungeon: Temple of the World Spirit

Nirrum has written volumes on the nature of this spirit

I, on the other hand, have written only a few paragraphs, despite having invented it.

When played a Shaman back in Dungeons and Dragons 4e, the only figurine we had for my spirit summon was a Translucent orange lego scorpion. It was the world-speaker spirit. When I started writing for my own campaign, I decided to include this as a force in my own world. Rather, I made it THE force of my own world. disconnected from the gods and the creators, this was the plane's magical immune system, built to contain a terrible eldritch force underneath a well-crafted but ultimately physical shape.

I wanted to introduce this spirit in an effective way, to tell the players why it wasn't active in helping them. I made it antagonize a yuan-ti settlement, made it force them to build this puzzle dungeon specifically so it could attempt to communicate to the players. I made it with the intent of proving that this creature, powerful though it was, was not capable of filling its function without help.

You'll need this, to begin

Temple of the World Spirit

 The entrance to the world spirit's temple is at the top. A huge bronze bell needs to ring to unlock the path inward. Underneath the bell is signs of a fire being lit such as a blackened bowl-shaped depression, some ashes and unburned wood. A small campfire burning for ten minutes will prepare the bell, allowing to be rung while it is still hot, the bell must be heated evenly, so one cast of heat metal won't be able to emulate the effects, though two sustained casts would. The bell rings for an unnaturally long time before anything happens. Quite suddenly, the central square block, containing the bell and the fire both drop downward, some parts of the block stopping earlier than others, making a narrow staircase that descends 100 feet before stopping. Ten Minutes later, the entrance resets back to normal.

Dm's Note: As an added bonus, the players have actually just crossed over into the Feywild. If you want to do some time-warp shenanigans, whether to catch them up with another group or delay them until another group catches up, this is a great place for some timeline changes. Torches that aren't part of the dungeon emit green fire and a low-pitched hum

The Purpose of the dungeon is for the world-spirit to communicate with the party the importance of safeguarding the bones against their destruction, thus, the world's destruction and the Freeing of Teruna. Thus The theme of this dungeons is Broken Prisons. The world spirit itself is trying to communicate its intent with them. This entire place was done with spirit magic. Creatures that die here find themselves in the Xanaran's at the end of the dungeon a few minutes later and are ushered into the stinger-opening without triggering the end scene.

This dungeon does not reset in any way, it was intended for the people who are now entering it. If they get clever and start breaking shit. Let'em. If they tunnel out of the dungeon, they're in feywild. Good luck with that.

DUNGEON STYLE

The dungeon is in the shape of a Scorpion with a Snakelike tail as if it were standing on a Dodecahedron (a d12). The tail is of a narratively infinite length but eventually pierces the hall of concept where it comes into contact with the claw Trochanters
The Dungeon's Colors are black, pale green, Gold, and pale pink.

It smells unnotable unless otherwise noted. The shadows are soft and the light is diffuse, unless otherwise noted. Sound echoes hard but poorly, the acoustics are terrible.

The walls and ceiling qualify as rather cheap but still striking semi-precious gems. The Doors are of magical quality and are immutable

The dungeon has black doors inlaid with gold filigree in the shape of a poem in abyssal, describing how the world-speaker should stay out of the way of the yuan-ti. The words are charged with magic that prevent the door from being damaged while it is in the feywild. The doors are large and their frames are hexagonal. They have no hinges but a handle on one side allows the door to be opened by rolling it sideways. Opening doors requires an action with a DC 11 Strength(Athletics) check. The doors are well-balanced but are mechanically Driven to close. Keeping them open for more than one round causes the DC to increase by 5 for every round that passes up to a maximum of 30, If the door is held open past this point, it breaks and remains open. Undoing the Door's Magic requires two checks, a DC23 arcana check to learn how to pause the magic and a DC15 Sleight of Hand to scratch the appropriate lines. The doors feel glassy with obvious changes in texture where the writing is.

DM's Note: The Doors close with enough force to bend steel and crush many forms of rock, but even that has its limits
Nirrum's Note: I can't help but notice that it is only the doors with these protections... I've got a few dwarves in mind for this dungeon

The Dungeon has Green Serpentine (Of course) Walls, with snakes in relief. The walls seem to smell of blood, or copper but none is present. The walls are nearly a meter thick at least. (but not indestructible if someone takes a pick to it, go to 20 if they escape). The walls feel glassy in all places where the carving has been finished, though occasional imperfections in the material will create a void or a small rough spot
The Dungeon is lit by wall mounted sconces of magical light. This light is sunlight. The sconces are shaped like Snakes which are trying to eat the source of the light.

The floors are pink Rhodonite. They are polished to Reflective. Below them is some extremely plastic but curiously mixed igneous bedrock, except where noted.

The ceilings are also rhodonite are are the same thickness as the walls unless otherwise noted and tend to be 15ft high, though the polish is far less clean

1) Antechamber

The first room of the world-speaker's temple only depicts a mural of The World Speaker . There is a door to the north(2), and unopenable doors to east(6), and west(9). The way the party came in is a large pit that seals with a square pillar in two minutes. The pillar slides upward, taking the bell with it. The pillar is rough, worn smooth in some places by imperfect setting, but largely it remains made of the same granite the rest of the outside of the temple is.

2) Hall of Concept

The hall of concept has four doors, North(9), East(3), West(6), and South(1).
A large, slightly curved Spike hangs from the ceiling, extremely close inspection reveals a tiny hole in the tip. The ceiling is a dome that is 50ft high at its peak, where the curved spike hangs.
This room is actually Unfinished. The walls are partially uncarved and a table sits near the North Door. The room is a dome that is 80ft wide

On the table is a small contraption. When a pin with a ring is pulled off of the contraption. The cheap string it was holding rises as a brass counterweight drops, pushing on a lever. There are two such pins and pulling on the second one lowers a second counterweight which pushes another lever, causing a tiny facsimile of a door to open on the contraption. The model can be picked up and interacted with but it is completely mundane.

Next to the table is a crate of dull chisels, awls, and punches. Next to that are eight broken hammer hafts. In front of the table is the skeleton of a Yuan-ti pureblood. A tarnished dagger is on the ground nearby, the first half of the dagger is rusted.
The North Door(9) is unopenable, though it has a handle that would indicate that it can be opened. Two sconces flank the door making that part of the room exceptionally bright. The Door only opens when both have gone out
The East(3) and West Doors(6) are both open

Dm's Note: This pureblood died when another yuan-ti assassinated her. The Pureblood had intimate knowledge about the dungeon

When the players re-enter the room after releasing both pins, sliding down from the ceiling above the north door is a cage suspended by two thick chains. Inside there is a Devourer (Volos138). It Breaks out and Chases the players and attempts to kill them. That said, if they try the now darkened North Door (9) it will open.

3) Left Trochanter and Femur

This room is decorated with a mosaic mural detailing the Timeline of the plane up to the cooling of the aegis and the return of life to the surface, and starts with the presence of Pelor. The beginning of this room is a round section that is closed off with bars. Normal steel bars. (They've got an AC of 15 and 20hp each). They are spaced 1 inch apart. The next 30ft is a long and flat section which contains most of the mural. There is a trap in the long section. A pressure plate near the middle which drops a 10x10x5 cage on whoever triggers it. The pressure plate does not take up the whole hallway, There is three feet on either side to allow people past. The person must make a DC17 dexterity saving throw or be trapped within the cage, if the creature caught in the cage is taller than 5ft, it takes 2d10 bludgeoning damage as well. The cage requires a DC 18 Strength check to lift. The door at the end of the hallway leads to room (4), the left patella

Dm's Note: Choose your own trapped square but choose it before they enter the room, it is a DC 16 investigation to spot the pressure plate but it requires thieves' tools to deactivate without force

4) Left Patella

This room is 30ft long, 10ft wide and Magically Darkened. The entire room is also covered in poisonous spikes which have poisonous barbs on them. The barbs are stationary but it is a DC17 dexterity saving
throw to not be punctured and a DC15 Constitution save to not be poisoned once you get poked by either a barb or a full spike.The spikes do 1d6 damage, the Barbs do 1 damage, and the poison does 1d10 damage and the creature is poisoned for one hour. There is a 2ft wide s-shaped Crawlway that a creature can crawl or crouch along with ease if it is able to avoid the spikes. At 10ft, 20ft and 25ft, the are barbed rods going across the hallway that stop creatures from standing that have the same effect as the barbs in the rest of the room.

Dm's Note: Devil's sight, a cane or staff or something to detect the danger with or even a 4th level cast of Dispel magic will remove most of this challenge. That's OK, there's more coming. Remember that Dexterity is body control, while strength is force output.

5) The Left Claw

The door to the left claw(6) from the Antechamber (1) is locked. It lacks a handle from that side.This room can only be entered from room (5). The Door to the Antechamber is one-way and only is able to be opened from this side and then, only after the Pin is pulled out.

The Room Is in the shape of an emperor scorpion's claw. Entering the room, one sees a hallway that is mostly straight and thin to their right. The hallway's left wall is jagged and approximately 60ft long. To the right there is a larger chamber, 65ft long, which has statues of an azer, a storm giant, a human wizard and a Tree. The Tree is notably a real tree with exceptionally white bark. Its roots extend through the podium base and out into the bedrock beyond and strangely seem to get thicker the further they are followed. The statues are placed in irregularly sized alcoves on the right wall of this hallway. The right wall is deeply curved. although the hallway ends rather narrowly, like the opposite hall. At the end of this pincer, there is a Bottle on a pedestal which should be identifiable as a potion of healing. In the deepest part of the curve, upon a small dais, there is a Pin made of Granite that is chained to a large Steel circle in the ceiling.

The pin is attached to a Vrock (mm64) via a 5ft chain that it cannot escape. The Vrock is extremely hostile. Removing the pin causes the steel circle to extremely rapidly ascend 20ft, revealing a hole in the ceiling through which 8 quasits(mm63) climb out, while also Freeing the Vrock to move around.

Dm's Note: This should go without saying, but it is an easier fight if they kill the vrock before taking up the pin. Punish them if they try to free it first. Focus down the kind-hearted, attack them first. The Vrock cannot get out itself. Magic. The demons just want to kill something, they don't care if they die.

Passing through the door at the end of this hall brings the players back to the antechamber(1), A sconce next to the north door In the hall of concept(2) has gone dark

6) Right Trochanter and Femur

This room is decorated with a mosaic mural detailing the Timeline of the plane during its creation and the sealing of the life-eating demon and ends with the presence of Pelor. The beginning of this room is a round section that is closed off with bars. Normal steel bars. (They've got an AC of 15 and 20hp each). They are spaced 1 inch apart. Similar bars drop down around the door handle six seconds after the door closes, preventing it from opening. A black pudding drops down upon the party. A DC 18 perception check on entering the room can spot the trap before it is sprung. The Black pudding takes 1d6 bludgeoning damage upon falling. The longer part of the hallway is 30ft long. Four Tripwires along the hallway trigger poisoned dart traps. It takes a DC15 perception check to spot either the holes or the tripwires. The resulting DC15 investigation check is made with advantage to figure out the trap, disarming it is not spectacularly hard. The darts attack with +8 to hit and do 1d4 piercing damage and a creature that takes that damage must make a DC 15 constitution saving throw or take 2d10 poison damage and be subject to the poisoned condition for 1 hour. The darts have a wide bladed top, thin center, and flights made of individual feather barbs.

Out of the image of a black and slim monster, a dart fires toward you!

The image, in question looks as a Wasp or stirge with sixteen eyes, a large stinger, an abdomen that appears to have two large holes in it such that it resembles a strange forearm, and a vaguely humanoid skull

Out of the image of a white tree whose roots spread across the mural, Another dart!!

The Trees roots run through the entire mural and in fact, seem to spread across the floor.

Out of the image of a pile of bones in the vague outline of a monster, A dart!!!

The Same monster as before

A dart fires from the image of the hand of Pelor!

The God of the sun looks smug

7) Right Patella

This room is 30ft along and 10ft wide and Magically Darkened room. Creatures with Darkvision of at least 90ft can see in this room as if it were dim light but creatures with darkvision of only 60ft cannot. Creatures with 120ft of darkvision can see as if they would in nonmagical darkness. The door at the end of the room leads to room(8)
Two shadow demons Attack

ROLL INITIATIVE, THE DARKNESS ITSELF SEEMS TO ATTACK

8) The Right Claw

Identical in shape to the left claw(4). The Door to the right claw(8) is only openable from The Right Patella(6). The Door to the Antechamber is one-way and only is able to be opened from this side and then, only after the Pin is pulled out.

The Room Is in the shape of an emperor scorpion's claw. Entering the room, one sees a hallway that is mostly straight and thin to their right. The hallway's left wall is jagged and approximately 60ft long. To the right there is a larger chamber, 65ft long, which has statues of the party, in intricate detail. Members of the party that are cursed, magical in origin, of a different plane, or have a spooky destiny might be made out of a different type and quality of stone. The statues are placed in irregularly sized alcoves on the right wall of this hallway. The right wall is deeply curved. Although the hallway ends rather narrowly, like the opposite hall. At the end of this pincer, there is a Bottle on a pedestal which should be identifiable as a potion of healing. In the deepest part of the curve, upon a small dais, there is a Pin made of Granite that is chained to a large Steel circle in the ceiling.

Touching the pin causes a magical chain to spring from it and attach itself to the creature that touched it unless they succeed on a DC18 Dexterity saving throw. If they fail, they are trapped in a magical chain that prevents them from using magic themselves, and drained of the strength to lift the pin. the chain shortens to 5ft long. The Pin does not react to ranged attacks. The pin can only contain one creature at a time and will alternate between multiple creatures if they try to push it at once. It takes a DC15 athletics check or 30 damage to lift the pin out of its hole. The steel circle in the ceiling slides up to shower dead bugs down on anyone below it. Anyone chained to the pin takes 2d6 bludgeoning damage as they are yanked up. When the chain stops sliding up, 10ft later, the person is released

Dm's Note: It was a poorly-thought-out trap. The Bugs had been deadly rot grubs when they were alive, but it turns out air and food are really essential for them. If the party does this claw first, then they will know to look at what might come out of the disk, If they do the left claw first, then the tension release from this humorous moment should be a good laugh and opportunity for role-play. I like this design duality. Get those who get hit by the bugs to roll a DC15 wisdom save or be frightened for one minute. Had this been two hundred years ago, they could have died.

Passing through the door at the end of this hall brings the players back to the antechamber(1), A sconce next to the north door In the hall of concept(2) has gone dark.

9) Prosoma

This squarish room contains Ten doors. One in the north(18), one in the south(2) and Four on Either side, east and west. For Brevity, these rooms are done in pairs. At one end of this room, Four blocks seem to be casting wall of force, preventing access to the next chamber to the north, the wall is pressed up against the blocks, teleportation inside the barrier is not possible. The Doors on the left are all locked.

10,14) Pair 1 - Petty Greed

Behind the first door is a large staircase which turns into a slide with a single twist, leading into the puzzle room. The slides are climbable but take a DC 10 Athletics check

The Monster chosen will be in a cage. The Cage is well made, but it seems to be holding down a chain on a pin, very similar to the ones in the claws. The Pin is welded into the cage. The Cage is bolted into the floor (with large hex bolts) and has a smaller cage in the middle, showing what appears to be 5 gold resting on the floor of the room, beneath the floor of the cage, The cage covers the passage forward. The bars are all half cut-through and a hacksaw is on the floor next to a Yuan-ti Malison skeleton which has a large serpentine rock buried in its skull. The room is a Pentagon with each side being 25ft long. There are other parts of other broken cages scattered around the room. The exit travels back up a set of stairs and then down a slide to the Prosoma(9) again.

Dm's Note: The catch here is simple. You can't progress Forward without dealing with the caged monster. But there are many easy and creative solutions to not have to deal with it! Not Dealing with it is actually the point and preferred answer. The chain, the bolts, wall of force, any of those good things! Heck, Even blasting it to bits while it's still in the cage is a great option. Free cage! but how will they get that gold? Oho

Upon completing pair one, Regardless of how the chain was released, one of the stones will have cracked along its length and the paired door will be unlocked. At the top of the stairs behind the normally locked door in this pair, is a bag of beans on a small shelf built into the wall

11,15) Pair 2 - Fear

The first door in this pair leads to a hallway that stretches evenly for a bit before turning around and into a staircase that leads downward in a somewhat shallow slope.

Here, in yet another pentagonal room, The party finds a pile of lumber (palm), another metal pin with a chain leading up to the ceiling, and some carpenter's tools. Upon touching the pin, a creature must make a D13 dexterity saving throw or be hit by a grey ooze (mm 243). The ooze follows players around the room and indeed, will follow them out of it if they don't figure out how to deal with it. This particular ooze will regenerate 10hp at the start of each round. The ooze seems less amorphous than others of its kind, and can't squeeze through any openings smaller than 2 inches at all. This pin is covered in runes similar to the doorway, A dc 13 Arcana check is enough to tell that the chain and pin are not immune to corrosion. Remember, Grey oozes can eat through metal but not wood. Do not be surprised if they capture the grey ooze

The door in this room will not open until the chain is dealt with.

Upon completing pair two, Regardless of how the chain was released, one of the stones will have cracked along its length and the paired door will be unlocked. At the top of the flight of stairs on the other side, before the party reaches the normally locked door is a set of Mithril scale armor, sized for a medium sized humanoid,

12,16) Pair 3 - Impending threats

Behind the first door here is a stairway down that doubles back on itself before becoming a short hallway which opens into a Strange set of catwalks. Upon Entering the room, the party sees more grey oozes being released from holes in the walls. They fall onto the catwalks and then The door on the other side of the room is not locked. In the center of the catwalks is a cage and behind that, The pin, which is behind held in place by a simple rod. The Cage contains a Nabassu (Mordenkainen's 135) which eyes the party hungrily. The cage is suspended above a room below which contains another Nabassu which appears to be Unconscious. The chains which suspend the cage are under attack by the grey oozes. It takes a grey ooze two turns to eat through a chain. Chains have 15hp and 18ac and a Damage threshold of 4. If the oozes succeed, the cage falls and the nabassu escapes, taking no falling damage

If they fail to stop the grey oozes from chewing through the chains, then they will fight two nabassu in the next pair. If they attack the nabassu on the floor below in any way, it attacks back, see below for special details.

The door on the other side leads up a similar staircase, and inset into the wall at the landing where the stairs switch back, is an immovable rod.

13,17)Pair 4 - Potential threats
The entrance way to this room is a very steep slide which twists once before reaching the bottom.

Part of the room described in pair 3(12), if they visit this one before pair 3(12), then twelve seconds in, a cage drops, releasing the nabassu from pair 3 (12) into the room, shortly followed by catwalks that the grey oozes begin to eat through 18 seconds in, and eventually, the grey oozes themselves.

There is a pin in this part of the room as well, but the Nabassu carefully watches it to make sure that it stays put. If the pin gets released, the nabassu gets imprisoned in a spherical wall of force one round later. If the second Nabassu is in the room, it will attempt to free the first by putting the pin back in. The pin's state is linked to the wall that stops progress into the tail (19)
The door on the other side is a long ladder which extends for short while before reaching another landing where another ladder points the other way. On this small landing there is a rope of entanglement

18) SECRET ROOMS -

by Using an action to make a DC 19 Investigation check in the Prosoma(9), the party can find two tiles side by side that can be lifted, each revealing a Different Secret entrance. One contains A Frost Brand Rapier (Pappenheimer hilt), and the other a cloak of Arachnida but instead of being able to cast web on the last ability, you can cast "ray of sickness". You also seem to glow bright cyan when in purple light while attuned to the cloak.

19) Mesosoma and tail

Having released all four barriers on the entrance, the way forward opens. The Party now stands on a precipice overlooking a vast and unfamiliar forest of Many-hued trees. To their right, the sun is just beginning to set. In front of them is a large barge. which sits on a deep and winding river around them. In fact, the whole temple behind them seems to sit in the middle of this river. Exploration of the outside of the temple reveals it as the shape of the world-spirit, whose legs are buried far underground. On the barge is a Spring Eladrin (Mordenkainen's 196) who hums quietly to himself.

"Welcome to the feywild! I've been waiting for you! I'm to be your boatelf!"
If the party has somehow avoided the dungeon such as by tunneling out without doing the paired rooms, the elf says "Oh dear, I don't think it'll be happy with that" and disappears without guiding them at all.

The Elf says his name is Elendaril Yuliran. He is friendly but will dive into the river and disappear if attacked. He is patient but excited. He acts as if something wondrous is about to happen and he's here to watch. He will always try to answer the party's questions and will attempt as best he can to help them get to the idea that the world spirit 1) is bad at communicating, 2) wants help keeping something locked up

"The World Spirit Sent me! Did you get their message?"

He explains that the spirit is in need of assistance and wouldn't mind some help. He tells them to hop on, as he can't stay much longer.

"All aboard! Yes all of you, and if you find any fey, don't accept any gifts from them, They'll want a favour later"
"Oh no! No no no, Keep your weapons out!" He says cheerfully if the party relaxes around him, "You'll probably need those"

The barge moves at 50ft a round

He explains that the spirit can't communicate in the normal way (poor thing), it's not made for it. Talking would just make it easier to corrupt. It communicates with magic in a rather clumsy way.

"Builds entire dungeons centuries in advance, schedules appointments with demons, Creates interplanar gateways and launches horrible challenges at people because it's literally incapable of processing a simple hello I need some help", says the elf, "Bonkers, really."

The elf is willing to interpret the dungeon if the players haven't figured it out but will only talk if they ask him

"Sounds like a lot of things you either had to avoid freeing or deal with afterward. Maybe it wants to keep something trapped?"

The elf will talk about each room, as they sail down the river, in this case, he will prompt them with "So Tell me about the temple!"

1)"Ah, I heard the bell when you folks came in"
2)"The spike in the ceiling is actually at the end of this river, but we'll get there eventually" "That demon sounds terrifying"
3) "Being imprisoned sucks! I imagine it took you no time at all to get through boring old metal bars."
4) "Like I said, It's not very good at communicating. You got through it though! Maybe that's the message!"
5) "Actions have consequences I guess? Look before you leap? Deal with one problem before you get more? Don't have a room full of demons if you don't have to?"
6) "Being trapped in a cage with a monster is bad! Not gonna take long before you or the monster wants out of that relationship" "The mural talks about how the plane was made, maybe it was important context?"
7) "You beat Two Demons... in the dark? I have a feeling it knew you could do it though"
8) "It's always a puzzle. The traps you've been through all seem to have been... well... beatable. You made it through them all and they were all ways to stop you"
9) "I forget if it was me or my three-times great grandfather who set up those runes. Wouldn't be able to tell you how it's done though. I guess it would have to be my grandfather.... Maybe it was my grandmother, I'm not certain, Time is messy here"
10) "Did you get the gold after? A demon is a demon but five gold is five gold. That's...over a hundred ales or 25 gallons of it at the local Xanaran's." "Of course there's a Xanaran's here. If I walked on the surface of the moon and didn't find a Xanaran's, I'd consider reality broken and the gods crazy. Not saying that those aren't true, but you get what I'm saying, There's always a Xanaran's"
11) "Ugh, Always with the Oozes, I hate oozes. I hope you managed to trap it or something"
12&13) "Nasty. I'm seeing a theme here though. Prisons are things you want to get out of but are kinda built to keep things in. If I was to bet, that's what the spirit is asking you. Keep something locked up because it's trying to get out. I wouldn't know though"
18) "HUH. REALLY?"

At some point, the elf will tell everyone to get on board if any are not, The smooth rapids and Dragontrees are coming up "And you don't want to be lost in this place! Filled with nasty things like Meenlocks and banderhobbs and Volos. And then the dragontrees, they're always so... BREATHY"
Dragon trees are trees which have similar abilities to Dragonbreath. They can understand (but not speak) Draconic but they are largely a belligerent and territorial bunch of plants that will not only duel with each other but frequently fire their weapons at anything that moves in their vicinity that they don't like, so communication was never an option. They are not fruiting currently and getting a sapling would be exceedingly dangerous

If everyone is on the boat he mentions the current picking up and says

"and you don't want to miss the main event"

And then A Marilith (mm61) launches from the forest onto the boat and the boats' pace moves to 120ft a round. All creatures in contact with the boat must make a DC13 dexterity saving throw or be knocked prone before initiative is rolled. A critical success here might see someone launched airborne in a favorable direction, A critical failure won't knock a creature off the barge, but might do 1 bludgeoning damage. Creatures that have proficiency with water vehicles make this save with advantage.

The ensuing encounter has some interesting twists. The Demon won't attack the Boatelf and the boatelf will only steer the barge down the river. The barge is 30ft long and wide, but has plenty of room to maneuver down the river. Every round, on Initiative count 20, The boatelf will call an element and a side or location. Roll a D6 and consult the list to determine which element Dragontree attacks the boat and where. The DC to avoid being caught in each will always be 14. Each Thing the boatelf calls will happen on Initiative 20 of the next round. So the players (and demon) have time to react.
Place [or side if fire or lightning is rolled]

1)Port-bow (front left) - [bow side (front)]
2)Starboard-bow (front right) - [Starboard (right)]
3) Port-Stern (back left) - [Port (left)]
4)Starboard-stern (back right) - [Stern (back)]
5) Center [Fire reaches to the middle, roll a d4 and consult above to see where it comes from, Lightning hits everyone!]
6) Roll again but the result deals 1d6 more damage!

Type

1)Acid splashes in a 15ft radius in one of the corners of the boat or the middle.
2)Lightning Shoots in a straight line across the boat, usually just one the sides.
3)Fire roasts the edge of the boat, or possibly reaches in toward the middle. Lighting flammable objects on fire
4) Cold leaves a 15ft area of the boat as difficult terrain as it freezes the water that's sloshed up. Creatures that move more than 5 feet across one of these slippery patches must make the save to avoid being prone afterward!
5) Poisonous clouds with a 15ft radius are shot swiftly at the boat but can't keep up. Make a constitution saving throw if you are hit by this or be poisoned for one minute as well as taking damage!
6) RAPIDS instead of a dragontree, Make the save to avoid being knocked prone, no other damage.

If a creature fails to save against the initial attack, they take 3d6 Damage
Copper Dragontree ahead! Looks like it's acid! Watch out on corner of the Port bow!

If you wish to call out the color of the tree as well as or rather than the element, use the Dragonborn subtype chart (PhB. 34) as a quick reference,

Falling off the boat means a creature is swept up in the current and must make a DC14 strength saving throw or take 1d6 bludgeoning damage on shallow rocks when they fall in and at the start of their turns until they get out. The creature then falls behind the barge, losing 5ft a turn. It takes a DC14 athletics check to swim up to half a character's swim speed toward the boat in these rapids, the boatelf will help anyone get back on. Tossing a rope off the side makes this a DC10 to get back. If someone helps pull a character back on, then no check is needed.

IF THEY ATTACK THE BOATELF, the party must make a dc 14 dexterity save to avoid being knocked prone every round as the boat bumps riverside. While prone, they make their save against fire and lightning with advantage and don't need to roll against rapids.The boat also slows to 55ft a round, A character swept up in the rapids needs to make the same DC to avoid pulling ahead of the boat. Poisonous clouds also last a full round in this scenario and lightly obscure the area they're in. Starting your turn or entering this space means you need to make another save!
A creature proficient in water vehicles can make an Athletics(Dexterity) check as an action with a DC of 12 on each of their turns to avoid this

At the end of the encounter, the barge bumps up a few times against the side of the river before coming around a bend where there is a pond with a few other boats made of folded leaves. The boats are docked at a Xanaran's. Barstomun Strongbeard, The Dwarf, is behind the counter, as usual but most of the glasses he has are shot glasses for the fairies that seem to be the sole patrons.

Ah good, adventurers. Do you want anything before you head on? Says Barstomun
I'll have a smidge of hot chocolate if you have any! Says the Boatelf if present.

Barstomun grants a 25% discount to all non-fey, including elves. He tells them that when they're ready to leave, to move the Wooden disc in the floor. Behind this disc seems to be a slide that curves out of sight.
Taking the slide brings the players back to the Hall of concept (2) through the stinger which enlarges to accommodate them.

Here the avatar of the world spirit awaits to reward them.
I'm giving these guys some magical tattoos, but now's the time to grant them a boon of some kind, some sort of Power ranger superpower
I'm also leaving behind some homebrew treasure:

Separation Beads

Whip, rare, Requires Attunement

This set of green translucent prayer beads reaches out to attack those you deem unworthy. The weapon has 6 charges, regaining 1d4+2 daily at dawn. When you go to make an attack, you can spend one charge to extend the reach of this weapon by 10ft for the attack. If you hit, the target makes a strength save versus your attack roll, becoming grappled on a save. The target can use its action to attempt to free itself by making a strength save versus the original attack roll.