Friday, May 30, 2025

Grotto of the Golden Gargoyle (Perils issue #7)

Pocket Sized Perils Issue #7 is here! 


It's been a hot minute since I posted here and even longer since I put out an adventure but here it is:

Grotto of The Golden Gargoyle 

clicking the pic above will take you to my page on itch.io 
 
This is the 'G' entry in the Pocket Sized Perils series (there's an alternate one hidden in the recesses of my drive that may join it someday).  I've made quite a few changes to the format and general approach this time around... 

1. It's system agnostic (not 5e)
2. It's less pocket sized (a longer PDF or print on demand book, as opposed to a fold'n'cut zine) 
3. It's more heavily OSR inspired than previous entries

Why not 5e? 

Like a lot of people, 5e was my entry point into TTRPG's and I have a lot of affection for it as a system. However since first cracking open the PHB  I've discovered there's a very, VERY, big world of games and gaming styles out there. I've dabbled with a bunch of different systems and in particular find myself gravitating to simple rules that facilitate creative play. That is to say; simple characters doing unique stuff together in the fiction rather than complex characters, (mechanically speaking), doing the same stuff, most of the time, regardless of the fiction.  I'm not dogmatic about it though. Fun is fun and different ways of playing have different strengths. 
 
 Why the longer format? 

 In exploring other modules and writing connected to ttrpgs I've really enjoyed the rich world building and detail some adventures or settings offer. Consequently I wanted to build more environment focused adventures, where parties could explore more and decide how to interact with the world rather than follow something like a three act arc. 

The work of Jennell Jaquays and Justin Alexander's writing about it was a particular inspiration. 
The Grotto was designed with loops (maybe too many), secrets, factions and verticality in mind. It's still a smallish dungeon but all those elements are present in some form.  

This is my 'goblins in a cave' adventure 
 
I just wanted to do it once - 'there are many like it but this one is mine'. Much like my soft spot for 5e I have a soft spot for trad fantasy tropes. I came to table-top games pretty late, so I still have a an itch to play with elements I've seen in fantasy in other media through my childhood. I'll definitely move on to weirder stuff from here but I can't go past G and leave 'Goblins' on the table. 

As a teaser for the adventure itself here is the goblin npc generator included in it: 

Sunday, November 5, 2023

A Wizard's Tower

A Wizard's Tower

 
 

I recently stumbled upon an image of a wizard's tower from one of my old home games. It was a fun environment for the players to navigate so I thought I'd pop it up here.

I often style my wizards as obsessively nerdy about a particular field. The wizard who built this tower is really into creating animal-human hybrids a la The Island of Dr Moreau. Continuing the Moreau theme I placed the tower on a floating island entirely populated by the wiz's bio engineered monstrosities. Even the plants were designed - as the players walked through the tangled mangroves I described the canopy of leaves turning in unison to catch the wind and steer the island on its mysterious course.

In classic mad scientist fashion the wizard has been eaten by rebellious frog people and their tower is... dormant. This set up left the players relatively free to poke around and put together the situation. 

From bottom to top here's a breakdown of the rooms. 

A Golden Barge

The Golden Barge



    The Golden Barge spools its way along a luminous thread through the humpbacked sky. 

On the prow, under the sheen of a translucent dome, tiny figures are moving…

 

I've been meaning to get into Troika by Daniel Sell for a while. The PDF has been sitting in 

my dropbox  but till now I've only rolled a few characters and enjoyed the art 

by Dirk Detweiler Leichty and Andrew Walter.

 
That changed this weekend when I set sail on a Golden Barge and dipped a toe into the system 

with a few friends. 

 

I'm pathologically unable to run a module in any system and couldn't help home brewing up a

quick one shot. Above is my attempt to map one of the Golden Barges eluded to by the rules 

(more than lightly influenced by Leichty's fantastic illustrations). I had hoped to actually make

 this post a rough outline of that adventure but I'd need to work further on my understanding of the 

system and the bones of the adventure itself for that to be worth your time. Instead, in the spirit of

Troika, I offer you this map as an invitation to your own imaginations. 

 

I'll include these two room descriptions I drafted for the session. 


The Kitchens
 

 

A fury of shouts and flames, a spicy assault on the senses - a cadre of inevitable chefs are busy cooking orders. 

They have been recruited from a fanatical culinary sect that will stop at nothing to spike any ticket that comes into the kitchen. An army might march on its stomach but these chefs will  lay waste to entire spheres to serve canapes. Only once a meal is served will they return to their  regenerative cocoons until service hours resume. 

 

The Hangar

It takes a lot to traverse the spheres. The assorted craft here aren’t up to the task - being more suited to 

a quick jaunt or occasional maintenance of the barge itself. The options in each bay are as varied 

as the passengers themselves. 

 

1. A Gossamer pleasure skiff - great for being seen whilst seeing the sights.


2. A large insectoid with mouth parts like a garbage disposal. Its compound eyes seem to shift from you 

to the saddle hanging nearby. 


3. A vapor ski - perfect for enjoying the humpbacked sky at the expense of everyone else.


4. A Scorpedo Rum Runner in jailbreak blue. There is a pistolet in the glove box and a person in the trunk. 


5. A two person, pedal powered, velocipede.


6. A Gronk class sky tug - solid as a bathtub full of concrete and just as maneuverable. 

 

 

 


 

 

 

 

 

 

 

 

 

 




Wednesday, July 26, 2023

Under The Dunes


Under The Dunes

 

    

 Another month another map and random table - like a serve of fish and chips or cheese and wine or... etc, etc.

There are mushrooms on this map, so here's a dual table to help you establish some fun mycology for players to mess around with. Also I'm aware a mushroom is the reproductive structure not the whole organism - it's just fun to say. 

What happens when you have a mushroom that grows dramatically when wet and an axe wielding murderbot in an adjacent cavern? I dunno - just asking the question.

 

What's That Mushroom Do?

Roll a d6 for an effect and what triggers it. 

This Mushroom...

  1. Soothes body and mind.
  2. Grants fantastic visions.
  3. Explodes violently.
  4. Induces sleep.
  5. Grows exponentially.
  6. Spreads Virulently.

When...

  1. Exposed to fire.
  2. Wet.
  3. Ingested.
  4. Touched.
  5. Combined with another fungus. 
  6. Subjected to any magic.

Friday, June 23, 2023

100 Strange Forest Encounters

 100 Strange Forest Encounters

 
 
I like random tables. I also enjoy simple, one page, dungeon illustrations that give you some game-able ideas at a glance.

So I'm going to start regularly posting some tiny dungeon images with a thematically linked random table. Once a month might be a good aim but let's see how we go.

The picture above is this month's tiny dungeon. I'm not going to go into detail about what the fruit thing is or the squirrel statue or the well of pure darkness. Does this dungeon involve Fruit Goblins? I don't know. Does it involve a swarm of undead squirrels that try and stuff you full of cursed acorns? Again, I don't know. Does drinking the well water give you a free spell that has a chance of progressively mutating you every time you cast it? Stop asking! But if you have a hollow tree or a hole in the ground in your game you now have this little doodle to go with it. 
 
Now to further explore the world of woodsy weirdness here are 100 things for players to run into when in a forest.
 

Thursday, December 17, 2020

Issue#6 Flaming Fandango in Faratusa

  Issue #6 Flaming Fandango in Faratusa

Well here we are - it’s the closing moments of 2020 and I’m spending my last spell slot to cast ZINE one more time.

I’m really not sure how many of the kickstarter backers out there found their way to these blog posts but if you’re one of them - thanks for taking a punt on these odd little adventures, I hope they’ve brought you and your players a lot of joy.

Let's roll up our sleeves and look at what we’re dealing with in Pocket Sized Perils Issue#6  Flaming Fandango in Faratusa.




 

Connections to other adventures

Since the hook in this issue revolves around a macguffin, (The Salt Ember Crown), the simplest way to link it to other adventures in the series is to change that macguffin. Here’s three options

  1. You can this link this adventure to Issue#5 Echoes of Ebonthul, by making the macguffin a piece of ancient technology the party brought back from that adventure - something that will protect the port of Faratusa from the threat of The Fire Chain Pirates. Perhaps Sir Aroldo has somehow swindled it off them and used it to weedle his way into the Governor’s good graces?

  2. If your group are interested in The Resistance’s struggle against the evil Baron touched on in Issue#1, you can make the Mcguffin a high tech weapon the Baron is trying to acquire from The Governor of Faratusa, or even a hostage NPC artificer/inventor being forced to design weapons. The masquerade ball can be reframed as a celebration of their successful deal and the The Fire Chain Pirates can be allies of/working for the Baron, (who never buys anything they can steal).

  3. If your group got pulled into some other realm in the final confrontation from Issue#5, The McGuffin can become something that might allow them to travel back. This requires reflavouring Faratusa as some sort of floating island port in whatever astral void the ritual at the end of Issue#5 lead them to.(I actually did this with one of the play test groups and it provided a lot of fun).


Now let’s jump into the zine itself.

The Hook


As always, the purpose of the first page of the zine is to set up the hook and get the imagination train rolling. We’re being a bit lazy here and letting the players fill in the details for our Mcguffin, (The Salt Ember Crown), and a potential ‘antagonist’, (Sir Aroldo Tuft). I’m trying to open up more and more of the creativity in my game to my players and this approach reflects that by letting them decide ‘why’ their characters are invested in this quest rather than me supplying them with a motivation.

The Plan

Once we know what we’re seeking and why we dislike Sir Aroldo so much we jump into planning our heist.

Page two feeds us a little background on the Governor and their obsession with constructs and gives us a narrow window to concoct a plan.


Depending on your group the time for planning can really blow out. This isn’t a problem if everyone’s having fun but if you want to keep things moving consider breaking up the planning into phases. One of my favourite mechanics from John Harper’s very slick, Blades in the Dark, system is the ‘flashback’, whereby players can step out of the flow of play for a moment to retroactively insert a bit of planning they ‘prepared earlier’. We can do something in that spirit for our adventure by letting the party plan in increments from objective to objective. When the party succeeds in getting the governor’s key or getting the crown you can give them another brief huddle to decide what the next phase in the plan is (and always was).

In the interest of keeping this closer to a one shot sized adventure, I've opted to start in media res with the player characters already in the building. If you don't mind things potentially running longer you can have them plan their way in, (just put guards on the gate and front door, a look out on the tower and roll for patrols everywhere else).


The Map






The specifics of the environment are important to this sort of adventure so this map (on the back of the zine) is intended to be shareable with your players. I’m trying to put more information in their hands and cut down on the need for detailed explanations from you as the DM


There’s more rooms and areas than are likely to be interacted with in a single play through to give the group a lot of room to plan their approach and also create opportunities for the architecture to play a part in the adventure via windows, stairwells, balconies and so on.


Perhaps the most notable ‘extra’ feature is the tower containing the recharge and repair stations for the Governor’s constructs. How is this meant to impact the adventure? I don’t know! It’s a bit of idea bait for your players. Perhaps they want to try sabotaging something here to disable the Brass Servants? Or maybe they’ll attempt to dress up in spare parts and impersonate them? Whatever the party may offer here, ask them to describe what they would like the result to be, identify the skill roll, (or rolls), you feel are required and follow where the dice lead you.


The Party



Hobnobbing with nobles in D&D is fun. In my experience players really enjoy getting the better of some pretentious aristocrat and watching each other put on their best, (or worst), courtly manners. Even before I knew a lot of other details about this adventure I knew I wanted it to include the opportunity for this sort of role play.


By placing the key to the vault on the Governor’s person we make it necessary for the player characters to mingle with the party guests to get it, (although they’re welcome to attempt to open the vault some other way).

In running this part of the adventure I would expect chaos and prepare to embrace it. The random table here is meant to assist you by providing some prompts for unplanned NPC banter.


The Security


On page four we meet our security detail. In this adventure I’ve opted for constructs to fill the roll of guards & servants, whirring and clanking down the Governor’s marble halls. The reasons behind this choice are

  • To add to the fantastic flavour of the adventure
  • To justify having one stat block for the entire mansion staff
  • The comedy element offered by role playing with -2 intelligence automatons
  • To avoid the discomfort of players choosing to murder flesh and blood servants who are just doing their job.


The Brass Servants are CR1. You’d need to get around 10 of them before the encounter turns deadly. I don’t give their exact numbers in the zine, (much like storm troopers in The Death Star, I imagine there’s always more of them than the heroes want to deal with). Any combat with them early on should include the risk of more arriving.

If you don’t find them intimidating enough you could give them a trait similar to pack tactics, (something like ‘Clockwork precision’), and allow them advantage when they have an ally adjacent to their target. In general however, the Brass Servants are meant to be cannon fodder - there are deadlier foes further down the line.


The Score


If the party succeeds in getting the key off the governor and dealing with the guards in front of the vault then all they need to do is wind up the clockwork mouse and it will pop into a hole in the wall and unlock it.


This runs dangerously close to being a puzzle. It’s not much of a puzzle but it’s obscure enough that the players may get it twisted in which case you could use wisdom/perception and intelligence/investigation checks to try and point them in the right direction.

The Gold’lem


Cautious players will scope out the vault before entering and possibly spot the glyphs. Reckless players will not and will awaken the Gold’lem. The Gold’lem is an animated pile of treasure and is pretty much a faster and more heavily armoured version of a Gelatinous Cube with extra damage immunities. It’s around CR4 and deals a suitable amount of damage for something that a cautious group should be able to bypass entirely. It’s intended as a consequence for rushing in without looking.

The Twist


I couldn’t finish a Dungeons & Dragons kickstarter without dropping a dragon on players at least once! Nagamerah is CR6, she’s essentially a young ‘white’ dragon with better mental stats and a climbing speed instead of a burrowing one to make her more classically a D&D Red Dragon.

If Nagamerah isn’t scary enough we also have some CR1 ninja pirates, with fire whips, jumping out of the crowd, one of whom is Aroldo, (our traitorous antagonist from page one).

This is a deadly encounter and, depending on how easy a time the party has had till now, it could be bad news for them. For this reason I'd suggest that Aroldo launches his coup when the party are still in the cellar or elsewhere in the mansion. This will give the group some space to assess the situation and decide how & IF they want to engage with it.

Beating the Fire Chain Pirates in a fight isn’t what the party came here to do - they came here to steal a treasure and embarrass Sir Aroldo. Depending on the situation they could attempt to sneak away with their prize…

However if the group decides they’d like to foil Arldo’s coup d'etat there are some elements they could try and exploit.

Rather than a pitched battle in the Grand Hall they could attempt to lure the Pirates or Sir Aroldo somewhere Nagamerah would struggle to follow (being a large creature).

There’s also Nagamerah’s chains. I only vaguely hint at lore for the Fire Chain Pirates in the zine but if we imagine them as airborne raiders, riding on magically bound dragons then breaking Nagamerah’s chains may turn her from a foe to an ally? At the very least she is likely to be a little upset at her former captors. Perhaps the last moments of the session will be a conversation with a dragon rather than a fight with one?

That’s it!


And so we’ve come to the end of this kickstarter. There’s still 14 more levels for D&D characters to reach and 20 more letters of the alphabet to cover but I’m going to take a short rest and roll some hit dice before I think about how I might go about that.

I’m keen to add some more generalised entries to this blog in the near future, (perhaps a bestiary and some loot tables etc), so stay tuned for that.

I’m also going to put the zines up for sale on Drivethru RPG and possibly Itch sometime in Jan so if you’re interested in that - that will be a thing.

To all of you who backed the kickstarter, ran the zines with your friends and sent me emails saying lovely things about them - Thank you, these adventures were small but the decision to share my creativity with strangers wasn’t, the supportive community out there made me really glad I took the plunge.

It’s goodbye for now but we’ll be meeting in a tavern to map out our next adventure before you know it.

Warmest Regards,

Brendan Barnett

 


Tuesday, September 29, 2020

Issue#5 Echoes of Ebonthul


Issue#5 Echoes of Ebonthul

Is anyone out there? It can be hard to know with lock down in my home state keeping us in our homes and in our heads, waiting for the day when we're free to rejoin the world. The people I used to see on a daily basis have become distant echoes and that counts double for strangers on the internet.

What was I talking about? Oh yes - Issue 5! It's done, so once again I'm placing the latest adventure in a little glass bottle made of internet and hurling it into the dark ocean of... ocean'y'ness?

Hooks

What's that? You want to know how to connect this adventure to the others? Well everything's connected...or nothing is... Let's see!
  1.  The Path of the Masked Mage, If you haven't resolved the mystery of the masked mage from Issue #1 this adventure provides a possible connection to that plot line. Lady Briarthorn had sent a another group to investigate the origins of her former captor but now that expedition has vanished. It's up to the party to locate them and find out what forces are behind their disappearance.

  2.  The Race is on! Sirona's library in Issue#4 is something of a time capsule - the perfect place to find a map pointing to the long lost island of Ebonthul. Unfortunately the scholar the party used to help translate it made a copy and set off on a rival expedition. They've had a weeks head start and if the party isn't quick they'll snatch up all the gold and glory for themselves.

  3. To the Rescue! If your party has become attached to a particular NPC in your campaign you could introduce this adventure by making them one of the missing persons whom the party are seeking.

As always choose a hook that will offer the biggest buy in for your table - now onwards to the adventure!

Pages 1&2 - A Start & The Sea monster!

These pages set up a simple hook for groups playing this as a one shot and then jump into some action. 

The Missing Adventurers

 I feel the elements of a game that players create themselves offer the greatest opportunity for engaging them. To this end the identity of each missing NPC is a blank space for your players to fill. This puts a little pressure on you as DM to weave their ideas into the session. For example - If one of your PC's is seeking a pious cleric with a drinking problem feel free to include a holy symbol and an empty bottle in one of the tents in the abandoned camp. 
 
The zine has spots for four missing adventurers; 1 Dead atop the statue, 1 hiding within the hold of the giant construct and 2 inside the Writhing Masses in the arcane engine room. You can always add more for larger parties by adding more Writhing Masses to the final combat or using an ancient diving suit to hide in the bilge of the giant construct etc.

The Sea Monster 


 

Once our missing adventurers are established we jump into the action. I like my players to occasionaly feel 'out of their depth'. Giant monsters can be good for that because they can be sooooo big they attack the environment rather than the party. This particular scenario is a bit of a bait and switch where we quickly replace our giant sea monster fight with a sinking ship skill challenge.  
 
The 'monster' is only going to stick around for two rounds but it's highly likely the party will sling some spells and abilities at it. To help with that here is a quick and dirty stat block.



 
After putting a hole through the parties ship the The Guardian dives out of sight, its task of keeping the interlopers away from Ebonthul accomplished. The possibility that it could reappear at some point  should instill a little fear in the group and add some tension to our adventure. 

A quick side bar on Armour & Swimming.

Logic suggests any character in armour that falls overboard is likely to sink like a stone. However it also suggests that a character is unlikely to be strapped into their armour whilst sailing. So do we drown our fighters and paladins or steal their plate mail? 

If it were me I'd risk losing the armour over the character. Then I'd place some armour within the abandoned camp for them to find. It could even be a mithral chain shirt or something similar belonging to the person they're seeking or that has been recovered from the ruins.

Page 3&4 Map of Ebonthul

Whether your party saved their ship or washed up exhausted and half drowned there are four locations for them to investigate within the ruins:

1. The Abandoned camp (Confirmation that our missing adventurers were here)
2. The Ziggurat with it's star covered door (A simple puzzle for the players to unlock) 
3. The Pit (an alternate way into the ziggurat)
4. The Statue (The key to the ziggurat and a clue to the fate of the missing adventurers).
 
Consider putting a telescope within the camp for them to find and through which they can examine the other locations nearby. This allows you to feed them a bit more information and guide their decisions about what to investigate next.

 Page 5 The Pit

Here I'm trying to offer the party an open ended challenge.  It's unlikely the entire party will have a high enough constitution to get through the flooded tunnel without drowning, (unless they find an air pocket). This is meant to prompt creative solutions from the players. There are  spells and other abilities that could negate this challenge and that's fine too - it just means a member of the group has a chance to shine and spends some resources ahead of the final combat. 
 

Page 6 The Statue 

The other way into the ziggurat is through the front door and that means climbing the statue, (although the party can't initially know this).
 
Falling from the top of the statue at level 5 could easily mean insta-death. This is intentional. The group don't necessarily have to climb the statue to progress through the adventure so this scenario lets them decide their own level of risk, (just be certain the players understand that risk).
 
As with the pit, the party may devise a way to reach the top in relative safety or their prepared spells and abilities may offer a shortcut. Either way their reward  is the sixth gem from the ziggurat door and the dead body of one of the missing adventurers. I've suggested rolling to see which invented NPC this is to maintain impartiality but go with your instincts on how the various players in your group will respond to having an NPC they just created killed 'off screen'.

Speaking of the dead body - There are lots of ways the clues sprinkled through the adventure could be interpreted. I'm going to offer you one sequence of events below but feel free to invent your own.

The Dead Sailor's Tale


You and your companions have arrived at the fabled island of Ebonthul. You're here to uncover lost treasures and make your fortune. Spirits are high as you make camp amongst the ruins.

As the days progress you can't shake the notion that a distant voice is talking to you, just beyond the edge of hearing. The effect is strongest in the shadow of the massive statue on the eastern edge of the ruins - the dark stone it holds aloft seems to swallow the light.

The leader of your expedition orders the stone retrieved from its lofty perch. The nimblest among you climb the statue with pitons and rope and manage to lower it to the ground. Many want to return home with this prize but the expedition leader claims greater treasures still remain and persuades the crew to stay a few days more.

Below the ziggurat you find the machine. Many are loathe to approach it, (not certain it isn't in fact a living beast), but your leader is unafraid. They seem strangely familiar with the instruments  within and order the stone brought aboard  - for safe keeping. 

Horror beyond horror - you have seen your companions transformed into monsters! You have glimpsed the writhing terrors nested within that accursed rock. You fled, taking the sixth star from the door and sealing them all below. You cut the rope on the winch that descends into the pit lest they try and follow you that way. Desperate for safety you climb into the palm of the statue where you cannot be easily surprised. The wound in your side throbs as your frantic pulse beats in your temples - the last thing you see is the stars wheeling overhead.

The Back Cover

On this page I give you a tiny random table to flesh out the setting a little. I imagine Ebonthul as the ruins of some sort of 'Future-Past'. The elements included here are trying to evoke a sense of familiar technology with a fantasy twist.

The Fold Out

So the party have made it into the ziggurat! We get a twist in our tale and discover the monster that attacked their ship is actually a gigantic construct. The conclusion of our adventure awaits inside...


 The Cargo Hold

Here we have 'treasure' and a missing adventurer hiding from their companions. 
 
This NPC's sanity is likely to be near breaking point and the party may have to work to get straight answers out of them, (You could give the player character who knows them advantage to do so). 
 
I haven't told you how much treasure is present here so the question is - How much treasure do you want your party to have? 
 
Level 5 is the beginning of the next tier of play as the party move beyond local adventures and start  playing a larger role in world events. Giving them some funds could help set up the next phase of your campaign and invite them to make some longer term plans. Remember though, instant fortunes don't go unnoticed.

Whatever GP value you decide to set for this horde here are some unique items you can include for added flavor.
  1. A highly sensitive Talking Mirror that makes all history checks with advantage but needs to be convinced that you'll appreciate the information before telling you what it knows.  

  2.  A Clockwork Bird that can be used to deliver short messages as per the animal messenger spell.

  3.  An air tight stone jar full of 'Red Sand'. If placed near a tiny, non magic, non living object for one minute the Red Sand will rearrange itself into an exact duplicate of that object, (this property doesn't function in darkness). After one hour both the duplicate and original disintegrate into red sand. The amount of sand and the size of object it can imitate increase with each use, (small to medium to large and so on). Keep it away from light! There are entire worlds that are now nothing but giant deserts of red sand.
     
  4. The Coral Crown. Whilst wearing this crown your clothing and hair billows as if underwater and illusory fish swim through the air around you.

  5. The Qinggong Spear (magic weapon - requires Attunement)
    Whilst wielding this item you can use the dash action to move in any direction, (including vertically). To change direction during this dash you must make contact with a piece of solid terrain such as a wall, rock, tree branch etc. If you are in mid air at the end of your turn you fall.

  6. The Mask of the Magic Eater (3 charges - requires attunement)
    When a creature you can see within 60ft casts a spell, you can use your reaction and 1 charge to force them to make a DC 13 constitution save. On a failure they take necrotic damage equal to 1d6 + the level of spell cast and you regain hit points up to the same amount.

The Control Room

This is the operational heart of the construct but I've disabled it so that your players don't drive it out of the adventure. If the party want to take control of this wondrous machine they'll have to deal with whatever is draining the power and that means heading to...

The Arcane Engine Room 

Here we find some creepy aberrations doing some crazy magi-tech stuff with a shiny black crystal. This ritual happens at the speed of plot and is always 5 rounds away from finishing at whatever point the party stumble across it.

I've put some curly mechanics into this fight so lets break them down.

The Writhing Masses are here to protect The Stone and hopefully buy enough time for its lair actions to make things interesting.

The Stone is the center piece of the encounter. If the PC's can destroy it whatever evil thing is happening here stops happening (more on that later). Be sure to use the spreading cracks and other details to communicate to the players that they are on a timer.

The stone has two things it can do to try and protect itself

  1. Pull characters from the engine room into it's weird demiplane.
  2. Spawn Passengers there to attack them and maybe cross back with them to the engine room if they make their next save.

You can describe your demiplane in any way that suits your game. In mine an alternate version of the engine room floated in a starry void amidst various 'flotsam' from the material plane. The Astral Sea or Limbo from DnD lore are closest to what I imagine.

The Passengers personify the threat the stone represents  - they don't just want your blood, they want your identity! I've built them to go down easily but become more of a threat each round.

I would spawn them in within movement distance of PC's but not so close as to force opportunity attacks if the PC's try to seek a better position.

The Passenger's Dark Mimicry trait causes attacks against them to have a 50% chance of hitting any PC they're grappling but what if more than one Passenger is grappling a character? I would play it something like the Mirror Image Spell  and assume the chance of hitting a PC diminishes the more monsters are grappling it, (this situation is already dangerous enough).

What if the party try to damage the machinery instead? 

One of my groups always looks for shortcuts and opted to smash the machinery 'charging' the stone in order to stop the ritual. This is the kind of creative thinking I don't want to discourage so I had to choose how to handle that.

If you like you can arbitrate the effects this might have in your game on the fly OR you can assume an attack on the machinery is an attack on the stone using the same AC and hit points  but narrating the effects as if it is the surrounding technology taking the hit (shhhh don't tell the players).

Victory 

If the party destroy the stone within 5 rounds then disaster is averted. They have a marvelous machine  full of treasure and have probably found the people they came here to find. The Guardian may or may not be in working order after the fight (and depending on what you want for your campaign from this point).

Defeat

In the zine I note that the end result of the ritual is the entire island of Ebonthul being transported to the Stone's nightmarish pocket dimension.

But why? What do the forces within the stone gain from this?

Here's one possibility for you to consider -

Long ago the mage-priests of Ebonthul destroyed the world! Not the world the party knows, not exactly, another version of it. So they tried to fix it by splitting reality in half. Now there were two realities. The one they broke got sealed away inside the stone along with all the nasty things that show up when you permanently damage the fabric of space time. The other world got to continue on as if the apocalypse had never happened. It was genius really - providing the nasty things never figured out a way to cross over and reverse the process...

So there you have it - either the party are triumphant and rich or they have some plane hopping craziness to endure to make it back home and set things to rights.  

I myself have one final battle to set the world of kickstarter to rights with Issue#6 Flaming Fandango In Faratusa - I'll see you then!