Maxwell's Demon (3.5e Monster)

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Author: Foxwarrior (talk)
Date Created: 10/25/11
Status: Quite so.
Editing: Clarity edits only please
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Maxwell's Demon

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Maxwell's Demon

CR 12

CE Medium Outsider (Chaotic,Evil,Extraplanar)
Init/Senses +5/Darkvision 60 ft., Blindsight 5 ft.; Listen +17, Spot +17
AC 23, touch 12, flat-footed 21
(+4 natural, +2 dexterity, +7 Shield)
hp 114 (12d8+36+24) (12 HD)
Immune Variable
Fort/Ref/Will +11/+14/+19
Speed 30 ft., burrow 30 ft. (Anti-Entropic), fly 50 ft. good (Anti-Entropic), swim 80 ft. (Anti-Entropic)
Melee Claws +16/+16 melee (1d6+2 piercing and slashing, 4d6 fire, 4d6 cold, 20/x2)
Space/Reach 5 ft./5 ft.
Base Atk/Grp +12/+16
Atk Options +2d6 sneak attack, Attack on the Run
Abilities Str 18, Dex 17, Con 16, Int 13, Wis 32, Cha 8
SQ Darkvision 60 ft, Evasion
Feats Shielded in Life, Attack on the Run, Assassination Training, Lightning Reflexes, Variant Toughness
Skills Appraise +16, Spot +26, Listen +26, Sense Motive +26, Search +16, Hide +18, Move Silently +18, Sleight of Hand +18, Disguise +14
Advancement 13-15 (Medium), 16-20 (Large)
Variable Permeability The Maxwell's Demon gets one of the following bonuses, and may change which one as an immediate action.
Light Permeability The Maxwell's Demon is immune to fire, cold, and light-based damage, and is invisible. However, his claws deal only half as much fire and cold damage.
Permeable Flesh The Maxwell's Demon is immune to physical damage, except falling damage. He is also immune to sonic, force, and acid damage. However, his claws no longer deal piercing and slashing damage.
Anti-Entropic Travel The Maxwell's Demon gains a 30 foot burrow speed that leaves no tunnel, a 50 foot fly speed with good maneuverability, and an 80 foot swim speed. His burrow and swim speeds do not allow him to breathe while underwater or underground.
Membranous Form The Maxwell's Demon can stretch himself thin across an opening of up to 30 feet square as a full-round action. Doing so makes himself a Huge target, and he can take no actions other than spend a full-round action to resume normal form or spend immediate actions to alter his Variable Permeability. However, while he is a membrane, he can choose to manipulate the environments on both sides of the opening (see below) instead of getting any Variable Permeability.

A sinister brown hunched person stands before you, clenching and unclenching its modest claws and glittering gold in the sunlight. Upon closer inspection, you can see that it is actually made out of tiny wooden doors with brass knobs which constantly open and close.

Membranous Form: When stretched across an opening, the Maxwell's Demon may alter the temperature and/or pressure of the two sides of the opening, by increasing one and decreasing the other. Doing so takes time dependent on the volume of the area beyond each side of the opening, independent of the volume of the area on the other side. Determine the volume of an area by accepting the first area with less than 1 square foot of ventilation leading to further regions (The Maxwell's Demon can eventually affect the further regions too, but doing so takes many times longer). A shift of one step takes 1 round per 5 ft. cube of space in the region. Once a region reaches the minimum temperature or pressure, it cannot be reduced further in order to heat up or pressurize the other region. When the Maxwell's Demon stops covering the opening, it generally takes as long for the environments to return to normal as it took for the Maxwell's Demon to change them.

Table: The Temperature Levels

Temperature Effect
-200° F As Extreme Cold, but 2d6 lethal and 2d4 nonlethal instead.
-50° F Extreme Cold
-10° F Severe Cold
30° F Cold
70° F Normal temperature
110° F Severe Heat
150° F Extreme Heat
190° F As Extreme Heat, but 2d6 lethal and 2d4 nonlethal instead.
340° F As Extreme Heat, but 3d6 lethal and 3d4 nonlethal instead, and constantly on fire.

Table: The Pressure Levels

Temperature Effect
Vacuum Risk suffocation, things can't catch on fire, and fire damage is halved.
Thin Air Take 1d6 points of nonlethal damage every 15 minutes from slow suffocation.
Normal Pressure Everything is fine.
High Pressure Sonic attacks deal +1 damage per die.
Very High Pressure Sonic attacks deal +1 damage per die, and have 50% increased range and area of effect.
Extreme Pressure Take 1d6 points of lethal damage every 15 minutes from internal hemorrhaging.

Strategies and Tactics

The Maxwell's Demon prefers to block the only exit to a structure and kill everyone inside by burning, freezing, or suffocating them. When approached, however, Maxwell's Demons shift back into normal form, and use their Anti-Entropic Travel and Light Permeability to eliminate their foes with effective hit-and-run strikes. If they judge that hit-and-run attacks are ineffective or unnecessary, they either run away or use Permeable Flesh to slaughter their enemies in relative safety.


The original Maxwell's Demon was "created" by an enterprising Elan Cleric named Maxwell, who, over the many millenia of his existence, slowly became obsessed with defeating thermodynamics. When the third god he worshiped was slain by a Balor Wizard, the backlash ripped apart his slowly decaying sanity and he turned to the Abyss for inspiration. He achieved his goal when a scroll mishap after a particularly long night of research and combat transformed him into a Demon. Some say that he, the first of the Maxwell's Demons, is still wandering the Abyss somewhere.

Others say that this story is complete nonsense. Citing old adventurer's journals, they claim that Maxwell's Demons are called that because they were originally discovered at the surfaces of "Maximum Wells", wells filled with superheated air compressed to be denser than iron.

Typical Treasure

2d6 × 500 gp in items that can reduce entropy.

For Player Characters

As a creature with HD equal to its CR and reasonable mental stats, it may make an acceptable PC.

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Foxwarrior's Homebrew (718 Articles)
Article BalanceHigh +
AuthorFoxwarrior +
Challenge Rating12 +
Identifier3.5e Monster +
NameMaxwell's Demon +
RatingUndiscussed +
SizeMedium +
SubtypeChaotic +, Evil + and Extraplanar +
SummaryScary monster that can control its permeability to energy and matter. +
TitleMaxwell's Demon +
TypeOutsider +