HARP Bestiary Preview Excerpt: Caustic Slime

Copyright John Duffield and Aurigas Aldebaron LLC © 2015

Edited by Peter Mork for The Guild Companion

"Some cities in the past have even cultivated caustic slime as a form of garbage disposal."

HARP Bestiary Preview Excerpt: Caustic Slime


Name Caustic Slime
Level 4
Size Large
BMR Type Worm/Snake
BMR 14
# Enc 1
Outlook Hungry
Treasure N2--
DB 10 (QU 10)
Hits 168
Init 5
Stamina 76
Will 71
Magic 26
Build Monster


Pseudo Palp - Medium Crush 84


Ambush (8) 68, Camouflage (8) 56, Climbing (8) 80, Endurance (12) 168, Perception (10) 72, Resistance - Magic (4) 26, Resistance - Stamina (8) 76, Resistance - Will (7) 71, Pseudo Palp - Medium Crush (12) 84, Foraging/Survival Underground (8) 36


Caustic Nature, Critical Resistance Major (Slash), Critical Resistance Major (Pierce), Critical Resistance Minor (Crush), Dark Vision (Greater), Electrical Immunity, Giantism (Minor), Immunity to Bleed, Immunity to Stuns, Multiple or Peripheral Eyes (Minor), Natural Climber, Natural Weapon (Pseudo Palp), Quiet Stride, Subtle, Susceptible (Fire), Susceptible (Cold)


Caustic Slime appears as a cloudy, viscous ooze which will cover an area of wall, floor or ceiling, even coating any furniture or other matter in an area. It favours damp, underground areas and the more observant and cautious can see that it moves at a slow pace, spreading slowly to engulf any organic matter it encounters. The surface of the ooze appears to have a flexible skin or rind while the interior is more fluid with small slow moving eddies able to be observed by those brave enough or stupid enough to get close to the being.

Slimes dislike fire and intense cold and will move themselves away from sources of both.


Caustic slimes are non-intelligent scavengers that haunt the depths of the earth, slowly moving across the damp underground looking for and digesting any organic matter they come across. Living and reacting from survival instincts only they have no particular preference for any form of food, as long as it is organic.

The slime can dissolve metals very effectively due to its caustic nature but it does not appear to do this deliberately nor are they attracted to metal objects. They do however dissolve any metal that they encounter as they move through their underground realm.

The slimes reproduction is normally the result of the slime becoming too large and splitting or by a smaller break away piece becoming separated from the main body and managing to survive.

Abilities and Combat

Caustic slimes when encountered are not aggressive and are content to move at their steady pace, though they will be ‘aware’ that the party represents food. If an opportunity is available to feed on the party the slime will do so. Normally this arise because one or more members of the party have either walked onto the slime as it was spread out across the floor, leant on a wall where the slime was or rarely, had the slime drop down onto them from the ceiling when it sensed food below it.

If a slime is attacked it will react violently, drawing back to create palp like appendages with which it strikes out, causing concussion and acid damage. The slime will fight until it is killed or the attackers have withdrawn from its reach.

The slimes attack delivers both a MA Strikes critical and an Acid critical one size smaller. A person coated in the slime due to either walking on the slime and being enveloped or having the slime drop upon them receives a Large Acid attack each round. Removing the slime is problematic and upon the slime being killed if the person is still coated they receive a Huge acid attack as the caustic matter slides off them and a small Acid attack each round for four rounds. Sufficient water will wash away this substance.

Electrical Immunity (30)

Slimes are immune to electrical attacks as they are able to earth the charge straight through them.

Susceptible To Fire (-15)

Slimes are vulnerable to fire and take double damage from fire based attacks.

Susceptible To Cold (-15)

Slimes are vulnerable to cold and take double damage from cold based attacks.

Immunity To Stun

Given their nature Slimes are immune to all stun damage.

Immunity To Bleeding

Given their nature Slimes are immune to all bleed damage.

Caustic Nature (20)

Because slimes are so caustic any weapons, armour and other materials that come into contact with the slime must make an RR or become corroded and useless. The RR difficulty is based upon the material being attacked and the wielder can add their Agility or Quickness as deemed appropriate.

Wood, soft leathers and similar organic material 140
Hard leathers, hard woods, stone, soft metals 120
Metals, magical woods 100
Magical metals, very hard metals 80

Note that enchanted items decrease the RR threshold by 20.


Caustic slime has been studied by a number of well-known mages across the ages, many looking for a useful application of its organic devouring properties. Some cities in the past have even cultivated one as a form of garbage disposal.

The slime appears to behave as a single entity though it is suspected that it is not so much a creature as a colony. The slime can separate out two to four smaller parts and often does so to feed effectively when food is spread out, though there is always a central mass which is larger than the two to four breakaways. It has been observed that if a slime piece is separated from the central mass by more than twenty feet or for a period of more than two hours the smaller mass often dies, though on rare occasions it will move on to become a new slime. Slimes do not digest materials such as gems and crystals so these can often be seen suspended within the slimes main body.

Races such as Dwarves have a particular hatred for slimes as they can both ruin and collapse structures by removing any wood used in the construction and they desecrate the Dwarven dead by invading burial tombs and dissolving them. Other races such as Orcs and Trolls will utilise slimes as a form of living trap by keeping an area stocked with food for the slime.

Adventure Notes

When a slime is killed it reduces to a clear liquid which is very caustic, creating a new danger for the unwary until it eventually neutralises itself over the period of an hour. The caustic material will eat into stone and other dissolvable material. However, if it is captured within a glass container of some kind the caustic material can be sold to mages and various craftsmen who use it for a variety of jobs. A vial of the material will fetch between eight and twelve silver. Do note that the use of fire or cold attacks destroys the slime in such a way that there is no left over material.

Cities with extensive catacombs or underground cities will hire adventurers to remove a particularly troublesome slime which has invaded and is causing problems. They will normally let the characters keep any loot found within the creature as a form of extra reward.