Large monstrosity, neutral

Armor Class 12 (natural armor)
Hit Points 103 (9d10 + 54)
Speed 40 ft.

15 (+2) 6 (-2) 22 (+6) 10 (+0) 14 (+2) 14 (+2)

Saving Throws Con +8
Skills Athletics +4, Stealth +0
Damage Immunities poison
Condition Immunities paralyzed, poisoned, prone, stunned, unconscious
Senses darkvision 60 ft., passive Perception 12
Languages Common, draconic (understands but can’t speak)
Challenge 4 (1,100 XP)


  • Absorb Arcane Energy. Any arcane spell targeted at an arcanoplasm is automatically absorbed into its body. This cures 1 point of damage per 3 points of damage the spell would otherwise deal; non-damaging spells cure 1 point of damage per spell slot used to cast the spell. Spells that affect an area are not absorbed, but neither do they affect the arcanoplasm. The arcanoplasm can’t absorb magic from spells that it cast itself using arcane spell mimicry, and it can’t absorb divine magic, which affects it normally.
  • Amorphous. An arcanoplasm can move through gaps as small as one square inch without penalty.
  • Arcane sense. An arcanoplasm can automatically detect the location of any arcane spellcaster within 100 feet. This ability is not blocked by any material.
  • Arcane Spell Mimicry. As an action, an arcanoplasm can mimic any arcane spell of 4th level or lower cast within 30 feet of it on its next turn. The spell takes effect as if cast by a 7th-level sorcerer (spell save DC 13, +6 spell attack bonus) and requires no components. Because of its innately magical nature, an arcanoplasm adds both its Con and Cha modifiers to concentration checks when it takes damage.
  • Immutable Form. The golem is immune to any spell or effect that would alter its form.


  • Multiattack. The arcanoplasm make one Slam attack and one Constriction attack.
  • Slam. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) bludgeoning damage plus 3 (1d6) acid damage, and the target is grappled (escape DC 12).
  • Constriction. One creature already grappled by the arcanoplasm takes 5 (1d6 + 2) bludgeoning damage plus 7 (2d6) acid damage.


Thought to be the result of a failed magical experiment, wizards and sorcerers alike have tried for years to gather information on this alien creature, but thus far such information has eluded even the most resourceful of researchers. Arcanoplasms are found in areas where the residual energy of arcane magic lingers. Such areas include abandoned wizard’s towers, keeps, dungeons, and so forth. Here they feed and remain until disturbed. Because it lairs in ruins and similar places that attract adventurers, it rarely has to wait long between meals. Arcanoplasms always target arcane spellcasting creatures first. Thanks to its ability to replicate spells cast near it, the arcanoplasm always tries to stay within 30 feet of a hostile arcane caster. Mimicked spells are cast at the foe deemed most threatening.

Section 15: Copyright Notice

City of Brass ©2018 Frog God Games; Authors: Casey Christofferson and Scott Greene

Tome of Horrors 2020, (C) 2020, Necromancer Games

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