Abyssal Custodian

Abyssal Custodian CR 18

This armored insectoid-crustacean has thick, spiked, shiny chitin and resembles a machine as it hunches over. Its thick tail subdivides into claw-like cerci.

XP 153,600
CE Gargantuan aberration
Init +8; Senses darkvision 60 ft., true seeing; Perception +31


AC 33, touch 10, flat-footed 29 (+4 Dex, +23 natural, –4 size) HP 290 (20d8+200)
Fort +16, Ref +12, Will +20
Defensive Abilities dimensional acclimation; DR 15/adamantine and bludgeoning; Immune cold, poison, fear; Resist electricity 30


Speed 40 ft., climb 40 ft., fly 50 ft. (clumsy)
Melee bite +29 (2d8+18), 2 slams +29 (3d6+18/19–20 plus push)
Space 20 ft.; Reach 20 ft.
Special Attacks dimensional plummet, push (slam, 20 feet)
Spell-Like Abilities (CL 18th; concentration +24)

At willdimension door, true seeing
3/day—create portal, quickened dimension door


The Abyssal Custodian is built for physical strength. It is heavily armored and highly resistant to most attacks. The abilities which render a custodian the most useful are its vast strength (custodians have been known to shove around starspawn with ease) and also its portal.

The Custodian’s Portal All abyssal custodians can open up a magical oneway portal to a nearby destination of its choice. This destination cannot be further away than about a mile. The portal is only visible on the custodian’s end, and nothing is seen at the destination, though detect magic can locate it.

The custodian can move through the portal itself as a means of travel, and thus show up elsewhere, suddenly surprising a group of enemies. A common use for the custodian in battle is to open the portal behind its enemies. It then uses its immense physical prowess to shove enemies through the portal to some special place—perhaps a dungeon cell, a canyon, or a walled prison compound—as its master commands.


Str 46, Dex 19, Con 30, Int 5, Wis 26, Cha 23
Base Atk +15; CMB +37 (+41 bull rush); CMD 51 (53 vs. bull rush)
Feats Awesome Blow, Critical Focus, Greater Bull Rush, Improved Bull Rush, Improved Critical (slams), Improved Initiative, Lightning Reflexes, Power Attack, Quicken Spell– Like Ability (dimension door), Staggering Critical
Skills Climb +26, Fly –10, Perception +31
Languages Aklo
SQ bound to master, no breath


Bound to Master (Ex)

An abyssal custodian is bound to a powerful entity, creature, or cult, and does all it can do to serve that bound master. If its master or cult is destroyed, the abyssal custodian becomes staggered until it gains a new master. At the GM’s discretion, certain rituals or other events can break this bond. Rituals to bind an abyssal custodian into service exist, but are rare, dangerous, and complex, and require the abyssal custodian’s consent (an abyssal custodian will never consent to serve a mere mortal such as a player character).

Create Portal (Sp)

Up to three times a day, an abyssal custodian can create an invisible, one-way portal, as per the gate spell, but only to a location within 1 mile of the abyssal custodian. This portal cannot be used to call creatures. True seeing or detect magic reveals the portal’s presence, but does not reveal what lies beyond the portal. The portal itself is thirty feet in diameter, and once created, persists for 10 rounds before vanishing. This ability functions as an 8th-level spell for the purposes of concentration checks and the like.

Dimensional Acclimation (Ex)

An abyssal custodian swiftly acclimates to changing environments after dimensional travel. If it begins combat by appearing via a portal or dimension door, it gains a +4 bonus on its Initiative check. An abyssal custodian is never disoriented as a result of using dimension door and is immune to effects that would banish it or otherwise forcefully transport it to another plane against its will.

Dimensional Plummet (Ex)

An abyssal custodian does not need to appear on a surface capable of bearing its weight when it travels via a teleportation effect like its portal or dimension door. If an abyssal custodian does not elect to begin flying immediately when it appears in midair, it can make a plummet attack on hapless creatures below. Treat this as a charge attack that allows it to make a single slam attack against any creature that is adjacent to its space when it lands. The abyssal custodian takes normal falling damage from a dimensional plummet. Any creatures that occupy the abyssal custodian’s space when it lands are crushed for an amount of damage equal to the falling damage the abyssal custodian endured. A Medium or smaller creature that takes this damage is knocked prone and pinned by the abyssal custodian. A Large or Huge creature is knocked prone and pushed into an adjacent space next to the abyssal custodian. An abyssal custodian that uses dimensional plummet to land on a Gargantuan or larger creature deals its crush damage as normal but has no other effect on the target, and the abyssal custodian itself is pushed into an adjacent space and falls prone as a result. A successful DC 30 Reflex save made by a Huge or smaller creature allows it to take half damage and be pushed into an adjacent square. The save DC is Constitution-based.


Environment any ruin
Organization solitary
Treasure standard

These entities were once just ordinary arthropods, like a terrestrial carrion or dung beetle, but this particular species dwelt in the homes of the Outer Gods. After millennia of feasting on the leavings and remains of the elder gods, they’ve grown to gigantic size. They are not particularly intelligent, and do not have much will of their own. These alien organisms evolved or originated from the same branch of life that gave rise to the mi-go.

They are clearly related anatomically to these fungi, though far more individually powerful. There is not just a single custodian but many, and other, even more formidable entities are known to import custodians to take on tasks for them. Whether or not they fight to the death depends on the will and instructions of their master. The death of a master breaks this binding, as do certain rituals. Custodians want to have a master, and when deprived of a master, they assiduously seek out those who know the proper ritual of binding.

The coloration of an abyssal custodian might range from a shiny metallic green, to bronze, to copper, depending on the type of god the creature fed from to reach its mighty size and strength. Its carapace is partly made of adamantine and other special materials.

The thickly armored thorax is sometimes a different color from the softer abdomen. The custodian has small delicate flippers so it can do tasks requiring fine manipulation.

An abyssal custodian is about 30 feet long and 14 feet tall.

Whatever its origin, every Abyssal Custodian encountered by player characters is serving a master. It always has a master, and this master is some entity even more powerful and dangerous than the custodian. In some cases, the master might not be a single being but an entire cult, a college of magic, or some other organization that together is potent enough to hold the custodian’s loyalty.

Abyssal Custodians are never found simply wandering around or “in the wild.” They are always set to protect and tend some structure or site.

Section 15: Copyright Notice

Sandy Petersen’s Cthulhu Mythos, © 2017, Petersen Games; Authors: Sandy Petersen, Arthur Petersen, Ian Starcher.

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