Expedition to Barrier Peaks – D&D 5th Edition Conversion (PART 4) – Pre-Existing Monsters and Custom Stuff

“I want to get off Barrier Peaks’ Wild Ride.”

EDIT: Many of the linked monsters no longer exist.  Plus, a lot of new monsters need an update.


Much of the art of conversion can be much more simple than one thinks.  Minimalism is something I’ve been meaning to toy with, as well as looking at my previously available options.  With that, here’s a list of existing monsters to modify for the adventure as well as creatures that already exist in some capacity.  Enjoy!

The following exist in previously published sources in some capacity:

  • Baboonoid (Use Ape stats) – MM P. 317
  • Black (Brown) Pudding – MM P. 241
  • Brilliant Fish – MM P. 338 (Use Quippers swam stats, add trait: Brilliance – Creatures within 30 ft. looking at them must make a DC 14 Intelligence saving throw or take disadvantage on attacks against them during their turn, increase Challenge to 2 – 450 XP.)
  • Bulette – MM P. 34
  • Couatl – MM P. 43
  • Displacer Beast – MM P. 81
  • Doppelganger – MM P. 82
  • Grey Ooze – MM P. 243
  • Green Slime – DMG P. 105
  • Intellect Devourer – MM P. 191 (Use stats: bump CR to 4 (1,100 XP), increase size to Small, increase AC to 13/Dexterity to 16 (+3)/Dex-based attacks to +5 to hit/+3 damage,  increase HP to 40 (9d6+9), increase save DC to 13)
  • Lizardoid (Use Tiger stats, make Medium size, make AC 13) – MM P. 339
  • Mind Flayer – MM P. 222
  • Scintillating Phosphorescent Fish – MM P. 338 (A DC 8 Nature checks results in knowing the spines are dangerous and can poison.  Use quipper swarm stats and turn their attack into “Spine”, which deals 1 piercing damage and the target must make a DC 14 Dexterity save or lose 1d4 Constitution until long rest.  Challenge increases to 2 – 450 XP)
  • Piercer – MM P. 252
  • Roper – MM P. 261
  • Shadow – MM P. 269
  • Shambling Mound – MM P. 270
  • Shrieker – MM P. 138
  • Spider, Phase – MM P. 334
  • Umber Hulk – MM P. 292
  • Violet Fungus – MM P. 138
  • Will O’ Wisp – MM P. 301
  • Yellow Mold – DMG P. 105

New Monsters: The following do not exist in the original module.  However, a crafty DM could always weave them somewhere into the adventure.  These were all made by me at some point in the past.  In addition, I’ve given some recommendations on where to use these and how these can be swapped with existing monsters.

  • Alien Menace (One or more can lurk throughout the ship, providing for suspenseful encounters.)
  • Augmented Cyborg (template) (Generic enough to be layered on top of existing monsters.  They can easily be put alongside robots or androids.)
  • Bonethief  (Works as a wandering monster.  For extra chills, have them possess a creature or two that are encountered.)
  • DOOM Monsters
  • Eldritch Ooze  (If the Bone Thief isn’t to your liking, this could work as a possible substitute for the Slithering Tracker.)
  • Elemental, Radiation (Areas of the ship plagued by radioactive materials are prime dwelling places for this creature.)  NOTE: This includes rules for handling radiation.
  • Greys/Fraal (Perhaps the original inhabitants of the ship haven’t completely died off!  It’s safe to say that they’ve probably gone mad though.)
  • Lurking Shade/Shadow Animate (Why not add some Doctor Who goodness to the ship?  The Vashta Nerada were one of my favorite monsters.  Having them … or an expy lurk in dark corners would make for a scary encounter.)
  • Newlithid Warmachine (There’s more of the Doctor’s enemies where that came from!  In the case of the module, this was likely a chained Illithid experiment gone REALLY wrong.  Either in a lab or cargo hold area.)
  • Psychic Vampire (Perfect for places where light is dim and things are eerily silent.  Much like the Xenomorph expy posted above, this one works for a great Alien-inspired scenario.)
  • Starving Thinker  (This wanderer is ideal for cramped corridors to amp up that survival horror mood, which is what inspired this one to begin with… in addition to Doctor Who, once more.)
  • Tormented Horror  (A creature of mad science, any prison containment area or laboratory is ideal for this creature.)
  • Vampire Variant – Astral Vampire (Basically the same monster as Psychic Vamp, but as a variant of the actual Vampire in the MM.)
  • Viral Lurker (Another lurker for many a sinister hallway.  Seriously, these creatures need a category all their own!  They’re an essential add-on for the Viral Undead.)
  • Viral Undead (Turn the ship into Sci-Fi Resident Evil?  Sure, why not?  Here’s another facet of survival horror gaming.  These sad saps can be shambling anywhere.)
  • Walking Disease (Likely something to emerge from the fungal outbreaks, that or an undead thing from the labs.  If you want some Last of Us flavor or a touch of Vault 22 from Fallout New Vegas, here you go!)


In addition, here are some brand new monsters made specifically for this post


Android, Gun Training

Medium Construct, neutral

Armor Class 16 (armor plating)

Hit Points: 66 (12d8+12)

Speed 30 ft.

STR 12 (+1), DEX 20 (+5), CON 13 (+1),INT 10 (+0), WIS 14 (+2), CHA 10 (+0)

Skills.  Acrobatics +8, Perception +8

Damage Resistances.  Bludgeoning/Piercing/Slashing from non-magical weapons

Damage Immunities.  Psychic, Poison

Damage Vulnerability.  Lightning

Condition Immunities.  Charmed, Frightened, Diseased, Paralyzed, Poisoned, Sleep

Senses.  Darkvision 60 ft, passive Perception 17

Languages. Common, Strange Alien Language

Challenge 5 (1,800 XP)

Gun Nut.  The Android has an assortment of guns at its disposal.  It may use a movement action to swap its weapon with another.  Roll a d8 to determine the gun and its effect:

  1. Pistol – deals piercing damage
  2. Laser Gun – deals “laser” (fire and lightning) damage
  3. Paralysis Beam – deals force damage, target must make a DC 13 Constitution saving throw or be paralyzed for up to 1 minute or until they succeed their next save.
  4. Machine Gun – deals piercing damage, target must make a DC 13 Dexterity saving throw or take an extra 7 (3d6) piercing damage.
  5. Radiation Gun – deals “radiation” (radiant and necrotic) damage, target must make a DC 13 Constitution saving throw or take 1 level of exhaustion.
  6. Force Blaster – deals force damage, target must make a DC 13 Dexterity saving throw or be pushed up to 20 ft. and knocked prone.
  7. Fire Shooter – deals fire damage, all flammable objects in burst of 5 ft. of target catch fire.
  8. Mind Eraser – deals psychic damage, target must make a DC 13 Intelligence saving throw or gain a short-term madness effect.  If they have already received such an effect within the last day, it becomes long term.  If this has happened with long-term, gain an indefinite madness effect instead.

Lightning Weakness.  When struck with Lightning damage, it must make a DC 10 Constitution saving throw.  If it fails, it is stunned until the end of its next turn.


Multiattack.  The Android may attack twice per round.

Firearm.  Ranged Weapon Attack: +7 to hit, ranged 60 ft./120 ft., one target.  Hit: 12 (2d6+5) damage.  Damage and effect are determined by the choices above.



Ghost in the Machine – Variant Ghost

  • This variant gains a new use for the Possession ability with Control Technology (listed below).
  • In addition, their Intelligence is increased to 18 (+4) and are trained in the Arcana skill (adding +7 to their skill check rolls).
  • They also have advantage on checks to identify foreign or mysterious technology.  (See Also: Dungeon Master’s Guide Page 268)
  • ACTIONS – Control Technology.  Instead of possessing living beings, this spirit prefers to manipulate gadgets and machinery.  The ghost must make a DC 15 Arcana check in an attempt to merge with the desired machine.  Upon success, the ghost can take 1d10 minutes to understand the item it is controlling.  Upon comprehending it, the ghost is considered proficient with this device as well as actively using it.  For example, if the ghost is inside of a laser gun, it can attempt to designate when or where it fires.  If there is another creature operating the device, the ghost and the other operator must do an Intelligence contest roll using the Arcana skill.  The victor can use the machine as they wish.
  • Its final Challenge rating is 5 (1,800 XP)



Metallic Ooze (Ooze, Nanite)

Medium Ooze, neutral

Armor Class 8
Hit Points 42 (5d8+20)
Speed 20ft., climb 10ft.
STR 16 (+3), DEX 6 (-2), CON 18 (+4), INT 10 (+0), WIS 8 (-1), CHA 1 (-5)

Skills.  Medicine +3
Damage Resistances acid, bludgeoning, piercing
Damage Immunities lightning, poison, slashing
Condition Immunities blinded, charmed, deafened, exhaustion, frightened, poisoned, prone
Senses blindsight 60ft. (blind beyond this radius), passive Perception 8
Languages –
Challenge 3 (700 XP)
Amorphous. The jelly can move through a space as narrow as 1 inch wide without squeezing.
Damage Repair.  Upon being reduced to 1/2 of its maximum hit points, it will regain 9 (2d4+4) hit points.  It will cease doing this once it has reached 1/2 of its maximum or above.

Healing Salve.  Melee Weapon Attack: +5 to hit, reach 5 ft, one target.  Hit: Target regains 9 (2d6+2) hit points.

Pseudopod. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 9 (2d6 + 2) bludgeoning damage plus 7 (2d6) necrotic damage.

Reinvigorate Corpse.  Some of the metallic ooze slips into a dead body.  1d4 rounds later, it rises as a nanite zombie.  For rules on recalculating a creature, consult the Dungeon Master’s Guide for the “Creating a Monster” section.  (Page 273)



Swarm of Gasbats

Large swarm of Tiny plant, unaligned

Armor Class 13 (natural armor)

Hit Points 60 (24d4)

Speed. 0 ft., 30 ft. fly

STR 6 (-2), DEX 12 (+1), CON 10 (+0), INT 4 (-3), WIS 6 (-2), CHR 2 (-4)

Damage Immunities. Poison

Damage Vulnerabilities.  Fire (see below)

Condition Immunities.  Blinded, Charmed, Frightened, Paralyzed,
Petrified, Poisoned, Prone, Restrained, Stunned

Senses. Darkvision 60 ft., passive Perception 8

Languages. –

Challenge 3 (700 XP)

Horrible Gas.  Any creature that starts its turn in or enters the swarm takes 3 (1d6) poison damage once per round.

Hovering.  This creature is always hovering, thus knocking it over is almost impossible.  Even if it is knocked out or paralyzed, it will hover in place.

Swarm. The swarm can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough for a Gasbat. The swarm can’t regain hit points or gain temporary hit points.


Multiattack.  The swarm may use its light slam attack up to 2 times per round.

Light Slam.  Melee Weapon Attack: +2 to hit, reach 0 ft., one target.  Hit: 9 (2d8) bludgeoning damage.

Noxious Gas (Recharge 5 or 6).  Melee Spell Attack:  DC 10 Constitution saving throw, 20 ft. range from Gasbat, all targets in range.  Failure: Target is slowed, as per the spell.


Explosion.  When the gasbat is within 10 ft. range of an open flame or magical fire, it causes the invisible gas cloud surrounding the creature to ignite and explode.  Creatures within 5 ft. of an exploding gasbat must make a DC 10 Dexterity saving throw.  Failure results in taking 18 (4d8) fire damage.  The Gasbat drops to 0 HP immediately.  Sometimes, gasbats will seek out fiery sources in a suicide attack on a target.



Swarm of Webbirds

Large swarm of Tiny beasts, unaligned

Armor Class 13

Hit Points 51 (34d4-34)

Speed 5 ft., fly 30ft.

STR 2 (-4), DEX 17 (+3), CON 8 (-1), INT 2 (-4), WIS 10 (+0), CHA 4 (-3)

Senses. darkvision 60 ft., passive Perception 10

Languages. –

Challenge 3 (700 XP)

Infect Host.  The target of a bite attack must make a DC 13 Constitution saving throw.  Failure: The webbird plants an egg in the target host, which hatches after 1 hour.  At the start of each turn following the grub hatching, the target must make a new save or takes 7 (3d4) damage as it attempts to consume them inside out.  After 1 minute following hatching, the grubs will burst from the host and attempt to fly off.  This deals the target 21 (6d6) piercing damage and 1 level of exhaustion.   Infants have the webbird’s stats, except they cannot infect hosts or create web.  2d4 hours after the grubs emerge, they become fully formed Webbirds.  A spell such as Lesser Restoration destroys the grubs and ends this effect.  Furthermore, a host that is currently infected or has been infected over the past 24 hours cannot be affected again.

Swarm. The swarm can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough for a Webbird. The swarm can’t regain hit points or gain temporary hit points.


Bites. Melee Weapon Attack: +5 to hit, reach 5 ft., one paralyzed/restrained/stunned/unconscious creatureHit: 5 (1d4+3) piercing damage

Web.  Ranged Weapon Attack: DC 13 Dexterity saving throw, ranged 40 ft., one target.  Failure:  The target is restrained and must take an DC 13 escape action to break free.  Slashing or Fire damage destroys the web, but will hurt the restrained target.



Vegepygmy Horde

Large swarm of Small plants, chaotic evil

Armor Class. 14 (natural armor, among other things)

Hit Points. 81 (20d6)

Speed. 30 ft.

STR 8 (-1), DEX 14 (+2), CON 10 (+0), INT 6 (-2), WIS 11 (+0), CHR 8 (-1)

Skills.  Acrobatics +5, Perception +3, Stealth +5

Damage Resistances. Bludgeoning/Piercing/Slashing from non-magical weapons; Lightning

Damage Immunities.  Poison

Damage Vulnerabilities. Acid

Condition Immunities.  Charmed, Exhaustion, Frightened, Poisoned

Senses.  Darkvision 60 ft., passive Perception 13

Languages.  ???

Challenge 5 (1,800 XP)

Fungaloid Stealth.  Double proficiency bonus (for a total of +5) when rolling stealth checks in plant-life or fungi.

Swarm. The swarm can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough for a Vegepygmy. The swarm can’t regain hit points or gain temporary hit points.


Multiattack.  The Horde may attack up to 3 times per round, using claws or spear

Claws.  Melee Weapon Attack: +5 to hit, reach 5 ft., one target.  Hit: 7 (2d4+2) slashing damage.

Spear.  Ranged Weapon Attack: +5 to hit, ranged 20 ft., one target.  Hit: 7 (2d4+2) piercing damage.

Russet Cloud (1/Day).  Ranged Spell Attack:  DC 13 Constitution saving throw, 5 ft. from vegepygmy, all non-plant based creatures.  Failure: 21 (6d6) poison damage, target contracts Moldies.  If the target is not cured within 24 hours, they die and dissolve into a russet mold patch 4d6 hours after death.



Zombie, Nanite – Variant Zombie

  • The Zombie’s AC increases by +2 (as natural armor)
  • The Zombie gains the Metallic Ooze’s Damage Repair ability, but it heals 4 (1d4+2) hit points instead.
  • Increase Challenge rating by one step.  In the case of the MM Zombie, CR 1/2 (100 XP)



Zombie, Irradiated – Variant Zombie  (NOTE: This uses the Radiation rules found here)

  • The zombie is immune to “radiation damage” (gain immunity to radiant and necrotic damage)
  • Gain a healing factor based on level of radiation the zombie is in (Gain cumulative 1d4+1 hit points for every step of radiation you’re in.  E.G. Light = 1d4+1, Medium = 2d4+2, etc)
  • Increase Challenge rating based on Immunity-based Effective Hit Points (Dungeon Master’s Guide Page 277)




**Major thanks to solomani for inspiration!

Made by Doctor Necrotic, for Doctor Necrotic Media.


Author: Doctor Necrotic

Hobbyist, amateur writer/screenwriter, wannabe-philosopher, music fan, history lover, cinemaphile, gamer, reviewer, and more. I'm a 30 year old hodgepodge of jobs and interests. My current projects on WordPress creating a wide variety of content for various tabletop roleplaying games, even showcasing published content here as well. When I have the time, I also create editorials and reviews spanning various bits of popular culture. I hope you take a moment to check my content out and maybe tell me what you think.

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