Dungeons & Dragons Online

One-Shot Adventure: The Gnome Initiative — Attack of the Mindcrawlers


The Gnome Initiative is a Fifth Edition adventure intended for three to six characters of 8th to 10th level and is optimized for a party of four characters with an average party level (APL) of 9. Characters who complete this adventure will earn enough experience to reach one-third of the way to 10th level. A mysterious island has trapped our brave adventurers, and they are searching for a way to escape. They stumble across a secret gnome facility that mind-controlling aliens are attacking. This adventure can be adapted to fit any campaign with a jungle island and another smaller island off the coast.

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Full adventure text below:


A mysterious island is traveling between the planes of existence and collecting creatures and people who find themselves trapped and unable to escape. With no way to escape, many of the island’s inhabitants attempt to dominate the rest of the creatures and people stuck there. Some try to make the best of their situation and build shelters, while others seek to understand the island’s nature and find a way back to their proper homes.

One such group calls itself the G.H.A.R.M.A. Initiative — Gnomes for Home And Restoration of Magical Apparatus. A band of brilliant gnome engineers, the Initiative has built multiple facilities around the northern part of the island to study its ability to phase between the planes in hopes of controlling it. They have developed a machine that taps into the island’s power and are close to creating a working portal.

They recently determined that one of the small islands off the northern coast is not, in fact, an island at all — it’s a derelict spacecraft that has been crashed there for decades.

After bringing some samples back to their jungle facility for study, the gnomes made a shocking discovery; the ship belonged to a species of mind-controlling beings that burrow into their victim’s minds and take control of their bodies — and they are still alive.

Adventure Hooks

Here are a few ways to get the adventurers involved in this story:

Mystery Island. Continuing their adventures while stuck on the mysterious island, the adventurers stumble across a gnome frantically banging at a metal bunker door deep in the jungle. He says his name is Valenzetti Pebblebottom, and he needs their help rescuing his people from the head engineer who’s gone insane.

Malfunctioning Portal. The adventurers are having a pleasant stroll through the countryside when all of a sudden they find themselves surrounded by flashes of light and crackling energy. They find themselves assaulted by the sights, sounds, and smells of a deep tropical forest and a string of curses coming from a small gnome standing next to a large metal bunker door. He introduces himself as Valenzetti Pebblebottom and begs their forgiveness for the rude summons — he needs help rescuing his people, and they are his only hope.

The Gertrudius Quadrilateral. Legend tells of a mysterious island that no one has ever returned from, hidden deep in the mysterious Gertrudius Quadrilateral. Hundreds of ships from both sea and air have entered, but none have made their way home. The League of Explorers (a vastly wealthy guild of explorers) wishes to hire an adventuring party that is powerful enough to take on any threat, find the island, and do what no one else has done before — return home safely.

After accepting an extravagant reward offer, the party enters the Quadrilateral and finds themselves on the mysterious jungle island’s sandy shore. But before they can even strike camp, they hear a loud banging and a string of curses coming from the nearby treeline. There they find a gnome beating on (and swearing at) a metal bunker door. Seeing the adventurers, he quickly begs them for their help and promises to tell them of a way off the island.

About the Mind Crawlers

The Mind Crawlers are a species of worm-like creatures with powerful psychic abilities. They start their lives as minute tadpoles until matched with a host body. These hosts take many forms, but all that a Mind Crawler needs is a living mind to take complete control, replacing the host’s personality completely. The tadpole worms itself into the victim’s brain and connects with it as it takes over its nervous system. The Mind Crawler then wipes away the host’s personality and takes over its memories and abilities.

A ship containing a Mind Crawler Queen and her entourage crashed on the island almost a century ago. The host bodies they inhabited were killed or too severely injured to leave their ship, forcing them to bide their time until the Initiative stumbled upon them. They’ve now taken over most of the Initiative members, worming into their brains and taking them over. The facility is now in a lockdown state initiated by the head engineer who barricaded herself in the control room.

About the G.H.A.R.M.A. Initiative

This band of gnomes found themselves on the island after crashing here on their airship over a decade ago. For years, every attempt they’ve made to leave the island has cost them lives, but it only hardened their resolve to get back home. They’ve built multiple hidden facilities across the island to conduct their experiments in peace from the isle’s randomness. Tapping into the island’s core, they’ve managed to create a machine that can mimic its planar travel ability to create temporal portals, but they haven’t been able to stabilize it yet.

Tristina Pebblebottom is the initiative leader and head engineer. She led the team that cracked into the Mind Crawler ship and brought the samples back to the facility she now finds herself trapped within. Her husband, Valenzetti Pebblebottom, was taken over by a Mind Crawler and was the only one to escape the facility before Tristina initiated the lockdown. She is now working to figure a way to save her people from the parasites.

The G.H.A.R.M.A. Facility

The underground facility of the Initiative is heavily fortified and has only a single way in or out. The initiative uses the facility to conduct their experiments on plant and animal life and provide shelter from the less hospitable island inhabitants. Multiple laboratories dedicated to different fields of study fill the complex from front to back.

The facility is currently in a state of lockdown initiated by the head engineer to trap the mind-controlled gnomes safely inside. One — Wilbos Pebblebottom— was able to escape but lacks the strength to fight through the facility’s automated defenses to break out the rest. The mind-controlled gnome now sits outside the entrance, raging against his new host body’s lack of strength.

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General Features

These general features are prominent throughout unless otherwise noted in the area description:

Ceilings, Floors, and Walls. The ceiling, floors, and walls are all smooth and clear of obstruction. Ceilings are 10-feet high throughout unless otherwise noted.

Doors. All of the facility’s intact doors are made of iron with hinges inserted into the iron door frames. They each have an AC 25, 20 hit points, and are immune to poison and psychic damage. The locks on these doors cannot be picked, and only pressing the properly attuned amulet to a small crystal panel inset next to the door opens them.

Lighting. The entire facility is well lit by glass globes along the walls enchanted with continual flame spells inside them.

Climate. The facility is powered through a combination of magic and steam from a natural hot spring the gnomes have tapped. This steam causes the entire facility to be even muggier than the jungle outside. Every 2 hours spent within this environment, each creature must succeed a DC 13 Constitution saving throw or gain 1 level of exhaustion. A short rest will remove all levels of exhaustion.

Clockwork Building. The facility walls are sheathed in riveted iron plating with cut-outs revealing giant gears at work within them. Pipes run the ceiling’s length carrying liquids and steam of all sorts; oddly colored condensation drips from them.

Mechanical Guardians. Within the facility are magic-powered clockwork guardians. These mechanical versions use the stat block as noted in the description with the following changes:

  • Type becomes “Construct.”
  • Languages become “understands the languages of its creator but can’t speak.”
  • Gains immunity to poison and psychic damage.
  • Gains immunity to charmed, exhaustion, frightened, paralyzed, petrified, and poisoned conditions

The Bunker Door

Whichever way the adventurers got onto the island and managed to meet Wilbos (see Adventure Hooks), they find themselves at the G.H.A.R.M.A. facility entrance with the mind-controlled Wilbos Pebblebottem (LE, male gnome mind crawler – see Appendix).

He imparts the following information but grows increasingly impatient the more prolonged the party delays entering the facility:

  • A mind-controlling creature has infected the head engineer, and it’s locked down the facility.
  • The facility’s mechanical defenses are targeting the gnomes trapped inside.
  • They have a machine that creates portals to other planes, and it is the only way to get off the island.
  • He can get the party inside but is “injured” and cannot go with them.
  • He draws a rough map of the facility to give to them, pointing out the central control room (area 13).
  • Once the party is ready to move forward, Wilbos will walk to the side of the bunker door and hold a rectangular amulet he wears around his neck to a small crystal panel. The door opens with a whir of machinery, and a flight of stairs leads down into the facility.

Keyed Locations

The following descriptions correspond to the provided map of the G.H.A.R.M.A. Facility:

1 – Entrance

A long flight of steps leads down from the bunker entrance into the facility. Large square iron panels cover the walls and steam spurts from pipes that line the ceiling’s upper edges. A metal box with a small panel on the western wall sits open with a thick metal wire dangling from it to the floor with tiny sparks shooting from the end.

Hazard: Electrified Wire. The wire from the wall panel has an electrical current running through it. Anyone touching it takes 9 (2d8) lightning damage. Someone must reconnect the wire to the proper slot inside the wall panel to automatically unlock the door to the Decontamination Room (area 3).

2 – Guard Room

Twin rows of upright stone and glass pillars stand in the center of this otherwise empty chamber. Half of the pillars appear to be heavily damaged by a portion of the ceiling collapsing; bits of stone rubble and metal panels have completely crushed two of them. Large suits of spiked plate armor stand upright in the undamaged ones.

Encounter: Mechanical Knights. There are three mechanical knights (use the knight stat block – see General Features). The Initiative built these clockwork and magic-powered constructs as the first line of defense for the facility.

3 – Decontamination Room

The door to this room from area 1 is locked (see “General Features”) and opens by fixing the Electrified Wire in that area. Metal piping converges on the ceiling into spouts that sit above twin rows of upright hollow stone pillars, partially closed off by ragged curtains.

Hazard: Acid Showers. Each of the stone pillars has a copper pipe leading up to the ceiling with a small iron handle that can be twisted up and down. If anyone standing in a pillar turns the handle, they must make a DC 15 Dexterity saving throw and take 14 (4d6) acid damage on a failed save or half as much damage on a successful one.

4 – Storage

The door to this room from area 3 is locked (see “General Features”), and the amulet found in area 8 will open it. Bits and pieces of shattered crates and containers lay strewn across the floor of this chamber. Intermixed with the debris is a cluster of broken and bloodied gnome bodies.

Encounter: Mechanical Guards. There are two mechanical knights (use the knight stat block – see General Features) and a mechanical gladiator (use the gladiator stat block – see General Features) in this room.

Treasure: Gems & Key Amulet. Searching the gnomes’ bodies will uncover a pouch filled with 10 emeralds (25 gp each) and a small silver amulet that is magically attuned to open the door from area 8 into area 9.

5 – Forge

A large pool of bubbling acid covers this room’s floor; a burst pipe in the ceiling feeds into it. A large, cold forge covers the eastern wall, and smith tools hang from racks on the walls. Bits and pieces of mechanical parts, gears, and large iron panels lay scattered across the room — most of them half-eaten by the acid. The corpse of a gnome lays half-melted across a large anvil in the middle of the pool of acid.

Hazard: Acid Pool. Anyone wading through the shin-high pool takes 22 (4d10) acid damage per 5 feet traveled as noted on the area’s map.

Treasure: Key Amulet & Hammer. A thorough search of the tools and a successful DC 15 Intelligence (Investigation) check will uncover an engraved magical hammer (has the same properties as a mace of smiting). There is a small silver amulet on the gnome’s corpse that is magically attuned to open the door from area 5 into area 8.

6 – Kitchen and D-Fac

The doors to this room are locked (see “General Features”) and attuned to the amulet found in area 8. Large wooden tables sit on their edges to form a protective barricade at the western end of the room. A group of gnomes armed with clubs made from broken chair legs and other mismatched arms huddle behind the flimsy protection.

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Gnome Engineers. There are half a dozen gnome engineers (mind crawlers – See Appendix) hiding in this room. If the party frees them before learning the truth, the gnomes thank them profusely for the rescue and encourage them to seek Tristina Pebblebottom, the head engineer. They quickly make their way out of the facility and to the jungle’s safety to meet with Valenzetti. If confronted after the party learns their true nature, they will fight to the death.

7 – Greenhouse

All doors in this room are locked (see “General Features”), and the western door is attuned to the amulet found in area 8; all the others are attuned to the amulet found in area 9. Rows of tables line the walls of this muggy room, topped with grow boxes filled with soil and exotic plants. A light mist fills the air from water sprayed through small holes in the pipes that stretch across the ceiling. The plant life has grown wild here, and it resembles the jungle outside more than the greenhouse it is supposed to be.

Exotic Plants. Anyone attempting to determine the various exotic plants’ usage and succeeding a DC 15 Intelligence (Nature) check will find a bush with berries that will heal 4d4+4 hit points when eaten. A creature can only benefit from this healing property once in a 24 hour, and there are enough berries for 3 uses. A failure results in them finding a bush with berries that will deal 4d4+4 poison damage when eaten.

8 – Petrification Lab

The doors to this room are locked (see "General Features''), with the northern door attuned to the amulet found in area 5, the western door to the amulet found in area 9, and the southern door to the amulet found in this room. Shattered glass and debris are scattered across the floor, mixed with ripped pages and puddles of unknown liquids. Broken statues of gnomes in different positions sit on chairs or lie shattered on the ground, all sharing horrified expressions carved on their faces. Racks of cages filled with the stone figures of various animals line the walls, and the smell of animal refuse lies thick in the air.

Encounter: Cock & Bull. There is a gorgon and a cockatrice rampaging in the room. In the chaos of the mind crawler’s takeover, the gnome scientists made an error, and the two beasts escaped but became trapped during the lockdown.

Treasure: Study Notes & Key Amulet. An active search of the paperwork scattered on the floor and a successful DC 15 Intelligence (Investigation) check will uncover some heavily damaged but legible notes regarding studying the mind-crawler specimen. They read as follows:

“The worm-like specimens brought from the ship seem to have a much more robust physiology than initially believed.”

“They’re not entirely deceased! We’ve managed to elicit brain function through the use of … (illegible)… and they’re responding! We believe they may be sentient…”

A small silver amulet attuned to the following doors lies around a gnome statues’ neck: all doors in areas 4 and 6, and the southern door in area 8.

Stone Gnomes. Only one petrified gnome is capable of being rescued with a greater restoration spell. Her name is Carza Sparklefeast (NG, female gnome priest), and the last thing she remembers is an announcement going out that a lockdown was commencing, and the next thing she knew, the gorgon was free. If she is freed before the party learns the truth about the mind crawlers, she will eagerly leave the facility to meet up with the other gnomes, only to be captured and made into a host. If she is freed after they learn the truth, she will try to help the party in any way she can.

Roleplaying Carza Sparklefeast

More stoic than is typical in a gnome, Carza is a cheerful and determined young woman who is a devotee of Hephaestus, the god of smithing and artisans. Part of her faith is to work towards sculpting masterpiece inventions in the name of her god. She is not fond of combat and avoids it at all costs; she will not travel with the party to hunt the mind crawlers but will instead want to secure the facility against their return.

9 – Living Quarters

The doors to this room are locked (see “General Features”), with the northern door attuned to the amulet found in area 8 and all others attuned to the amulet found here. Anyone listening at any door to this room can hear the golem inside pacing back and forth, crashing into things.

The broken remains of bunk beds, chests, and wardrobes lay scattered on the ground and crushed underneath the hulking feet of a large golem pacing this room. Many of the continual flame sconces on the walls have been shattered and leave the room dimly lit. The crushed bodies of gnomes lay intermingled with the remains of the furniture.

Encounter: Stone Guardian. A stone golem was activated to defend the facility and was trapped here during the lockdown. It laid waste to the mind-controlled gnomes here and is now decorated with their blood.

Treasure: Coins & Key Amulet. A careful search of the room uncovers a small silver amulet attuned to the doors in areas 7, 8, 10, and here. A collection of coins, jewelry, and valuables can be collected from the remains of the gnomes and their personal effects: a small silver ring inset with a ruby (400 gp), a golden chain necklace (12 gp), a bronze statue of a tiger inlaid with ebony stripes (70 gp), 326 gp, 457 sp, and 298 cp.

10 – Engine Room

The doors to this room are locked (see “General Features”) and are attuned to the amulet found in area 9. Large iron gears spin in the walls and spaces in the floor and ceiling, being pushed and pulled by whatever power is operating the facility. Steam hisses from open vents, and a deep thrumming rumbles through the floor.

Gnome Engineers. There is a trio of gnome engineers (mind crawlers – See Appendix) hiding in this room. They quickly make their way out of the facility to meet with Valenzetti.

11 – Head Engineer’s Office

The door to this room is locked (see “General Features”) and attuned to the amulet found in area 9. Schematics and plans of all types lay scattered across a large desk, held down by thick tomes. Papers lay haphazardly thrown onto every surface of every shelf and table in this room. A large chalkboard sits on the wall behind the desk, covered in equations and mathematical theories.

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Mathematics. Anyone who attempts to decipher the mathematics on the chalkboard and succeeds a DC 20 Intelligence (Arcana) check will uncover that they relate to calculating locations between points during planar travel. A pattern of numbers keeps repeating throughout the algorithms “4, 8, 15, 16, 23, and 42.”

Secret Door. Anyone actively searching who succeeds a DC 15 Intelligence (Investigation) check will find the hidden latch that swings open the bookcase leading to area 11a.

11a – Numbers Room

Smooth iron panels cover every surface of this otherwise empty room. A single sconce enchanted with a continual flame spell sits above a small metal box that protrudes from the otherwise smooth southern wall. The protrusion consists of two rows of numbered dials, a red button, and a slot; the top row of dials seems to be counting down, a loud click accompanying every shift of the numbers.

The Numbers Game. Regardless of when the adventurers enter the room, there are exactly five minutes left on the countdown dial. If no one enters anything into the second row of dials, the color of the continual flame sconce turns red once a minute remains, and the floor of the room begins to vibrate slightly. Once the dial reaches the last 10 seconds, the sconce starts to flash on and off, and the rumbling increases. If nothing is entered and the dial reaches 0, the light turns off for a few seconds before flicking back on to its standard color, and all rumbling ceases — the machine is now inert and will not function at all.

Entering the numbers “4, 8, 15, 16, 23, and 42.” and pressing the button before the countdown reaches 0 will result in the sconce flashing a bright blue color and all of the dials starting to spin rapidly. If it was not already rumbling, the room begins to shake for a brief moment. The room settles down, all of the dials then reset to 0, the sconce returns to its standard color, and a single random card from a deck of many things slips out of the slot, dealt to the one who entered the numbers. Redraws are not possible, and the machine is now inert and will not function again.

12 – Planer Lab

The northern door to this room is locked (see “General Features”) and attuned to the amulet found in area 9.

Once the adventurers reach this chamber, read the following aloud:

The iron door swings open into a scene of wonder — the floor and ceiling of the underground complex disappear, replaced by a swirling vortex of stars and space, enclosed within thirty-foot-high clockwork walls.

Standing in the center of this spiraling display of light is a giant mechanical monstrosity. A gnome woman is furiously climbing into a seat at the top. “You’ll never take me alive, you parasites!” she bellows as the machine closes around her and whirls to life with a clanking of gears and flashing lights.

Encounter: The Head Engineer. Tristina Pebblebottom (LN, female gnome mage) is riding in a Gnome BattleMech (see Appendix). She does not have any remaining spell slots to use for the day. Once the BattleMech is defeated, unless the adventurers succeed a DC 18 Charisma (Persuasion) check, she will fight to the death. If they convince her, she angrily tells them the truth of the situation (as outlined in the journal found in area 13) and implores them to go to the derelict mind crawler ship, help rescue her people, and stop them from using the stolen portal machine. She refuses to discuss any of the work they have been doing (including the numbers machine in area 11a) and pushes the party to make haste before it is too late.

Treasure: Power Gem. Two red corundum elemental gems are in the BattleMech remains. If Tristina is still alive, she will pull them out of the BattleMech and give them to the party to assist them once they promise to help.

13 – Control Room

If Tristina is alive, she will not allow the party to enter this room. This tiny chamber holds a collection of levers, buttons, dials, and colorful crystal screens along every surface of the walls. Lights flash from colored crystal gems, and the floor vibrates with the faint hum of what must be a massive machine below. A small desk sits against one wall filled with papers and an open leather-bound journal.

The Truth. The journal belongs to Tristina Pebblebottom and tells the story of how the gnomes first came to be on the island, their mission to tap into its teleportation ability to get back home, the discovery of the mind crawler ship and its location, and the subsequent siege as the mind crawlers took over the facility and stole the prototype planar travel machine.


After defeating Tristina and learning the truth about the mind crawler’s domination of the Initiative gnomes, the adventurers must decide if they wish to pursue them to their ship or not. If they choose to follow them, they will find brutal battles with all sorts of creatures as they fight through the massive ship to reach the Queen and the gnome portal machine.

If the adventurers failed to defeat Tristina or decide not to follow the mind-controlled gnomes to the ship, the mind crawlers use the gnome device to summon monstrosities as their new hosts. The once dying race enters a resurgence, going from plane to plane and dominating the races in an interplanar war that lasts for millennia.


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