Ferrofluid Magnetocluster

Large ooze, unaligned

Armor Class 17
Hit Points 189 (18d10+90)
Speed 20 ft., climb 20 ft. (magnetic surfaces only)

24 (+7) 18 (+4) 20 (+5) 1 (-5) 6 (-2) 2 (-4)

Skills Stealth +9
Damage Resistances lightning, bludgeoning from non-magic weapons
Condition Immunities blinded, charmed, deafened, exhaustion, frightened, prone
Senses blindsight 60 ft., passive Perception 8
Challenge 12 (8,400 XP)


  • Demagnetization. If the ooze takes any fire damage, its Magnetic Field and Magnetic Leap abilities do not function until the end of its next round. Additionally, any grappled or engulfed creature is immediately released.
  • Magnetic Field. Any creature who makes an attack using a ferrous weapon within 30 feet of the ooze must make a successful DC 17 Strength saving throw or gain disadvantage on the attack.
  • Magnetic Leap (Recharges 5-6). As a move, the ooze can move adjacent to a creature within its magnetic field that is either ferrous or wearing or wielding substantial ferrous equipment (iron armor or a greatsword would qualify, leather or bronze armor, or one dagger would not). This movement does not provoke attacks of opportunity. The ooze then automatically grapples that creature. If the target is a Medium or smaller creature, the target is also engulfed and suffers Blinded, Restrained, and is unable to breathe. and it must succeed on a DC 15 Constitution saving throw at the start of each of the ooze’s turns or take 13 (2d8 + 4) bludgeoning damage. If the ooze moves, the engulfed target moves with it. The ooze can have only one creature engulfed at a time.
  • Polarity Shift (1/day). As an action, the ooze emits a magnetic wave. All creatures within range of the ooze’s magnetic field must make a successful DC 17 Dexterity saving throw for each ferrous item carried or it is dropped in an adjacent square. Each creature wearing ferrous metal armor must also make a successful DC 17 Constitution saving throw or be knocked prone.


  • Multiattack. The ooze makes three attacks.
  • Pseudopod. Melee Weapon Attack: +11 to hit, 10 ft. reach, one target. Hit: 33 (6d8 + 6) bludgeoning damage.


Ferrofluid oozes can form virtually anywhere, but they are drawn to urban areas filled with magnets and ferrous metals and find solace in any place that thrums with electromagnetism. Their dark, aqueous bodies skulk low to the ground, and they often hide away beside magnetic machines in industrial districts or aboard starships and space stations. A few lucky oozes find caverns of naturally magnetized ore. Wherever the oozes travel, their magnetic properties reduce the vibrations of their movement, making them difficult to detect until their magnetic fields and unmistakable magnetic pull betray their presence. Ferrofluid oozes are usually about 3 feet in diameter.

While not inherently ill meaning, ferrofluid oozes often are at odds with the owners of the magnetic objects they covet. Usually utterly indifferent to organic life, ferrofluid oozes seek only to collect magnetic material— though they do defend themselves, and can attack when stubborn life-forms refuse to relinquish their magnetic goods.

Ferrofluid oozes that collect a large amount of debris are even on occasion mistaken for scavenger slimes.

Magnetic Propagation. As ferrofluid oozes skulk around places profuse with magnetized materials, they occasionally leave behind droplets of magnetic fluid.

So long as these droplets remain in the magnetized environments provided by their parent, their size and magnetic power grow in parallel with their access to additional magnetized material.

Due to this propagation, it is not unusual to see several ferrofluid oozes enjoying the same magnetically charged environment, so experienced adventurers are wary when they find only a single ooze in such a place. Given enough time and magnetic material, multiple oozes can form into a single, much larger ferrofluid magneto-cluster around 8 feet in diameter.

Section 15: Copyright Notice

Mechanical Monsters (5E) © 2023, Legendary Games; Authors: Jason Nelson, Miguel Colon, Robert J. Grady, Nicholas Hite, Matt Kimmel, Michael Mifsud, James-Levi Cooke, Dan Dillon, Mike Myler, Ismael Alvarez, Jeff Lee, John Lynch.

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