Ion Slime

Small ooze, unaligned

Armor Class 13
Hit Points 112 (15d6 + 60)
Speed 20 ft., swim 20 ft.

10 (+0) 17 (+3) 18 (+4) 2 (–4) 4 (–3) 1 (–5)

Skills Stealth +6
Damage Vulnerabilities cold
Damage Resistances thunder
Damage Immunities acid, lightning
Condition Immunities blinded, charmed, deafened, exhaustion, frightened, prone
Senses blindsight 60 ft. (blind beyond this radius), passive Perception 7
Challenge 5 (1,800 XP)
Proficiency Bonus +3


  • Amorphous. The ion slime can move through a space as narrow as 1 inch wide without squeezing.
  • Ionic Form. Whenever the ion slime is subjected to lightning damage, it takes no damage and instead regains hp equal to the lightning damage dealt. The slime’s Supercharge action then recharges. If the ooze takes cold damage while supercharged, it must roll a d6. On a 1 or 2, it loses the supercharged state.
  • Ooze Nature. The ion slime doesn’t require sleep.
  • Spider Climb. The ion slime can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.


  • Multiattack. The ion slime makes two Pseudopod attacks.
  • Pseudopod. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) bludgeoning plus 9 (2d8) lightning damage.
  • Discharge (Supercharged Only). The ion slime sends a shock of lightning through its supercharged pseudopod at one creature it can see within 5 feet of it, ending the supercharged state. The target must make DC 15 Constitution saving throw, taking 27 (6d8) lightning damage on a failed save, or half as much damage on a successful one. Three bolts of lightning then leap to as many as three targets, each of which must be within 20 feet of the first target. A target can be a creature or an object and each can be targeted by only one of the bolts. Each target must make a DC 15 Constitution saving throw, taking 13 (3d8) lightning damage on a failed save, or half as much damage on a successful one.


  • Charged Motion (Supercharged Only). The ion slime takes the Dash or Dodge action.
  • Supercharge (Recharge 5–6). The ion slime gathers ambient electricity to supercharge itself for 3 rounds. While supercharged, the ion slime gains a +2 bonus to its AC, and it gains an additional action on each of its turns. At the end of the third round, if the slime hasn’t used the Discharge action, it suffers feedback, taking 18 (4d8) force damage. Its supercharged state then ends.


A dull grey blob slogs through the submerged corridor. As it passes over a hidden lightning rune, it sparks to life, pulsating electric blue and becomes supercharged, racing around the hall.

Ion slimes are oozes born from magic-infused saltwater, questionable alchemical operations, or cast-off swamp lightning from foxfire oozes. With compact forms and coloring that reflects the current positively or negatively charged state of the ooze, ion slimes can be difficult to spot when submerged. Whether manmade, magical, or from naturally occurring bioelectricity, these wandering dynamos seek out and feed on electrical energy.

Forms in Flux. An ion slime lives most of its life in a negatively charged, dampened form. While in this form it moves sluggishly and with a hungry, searching curiosity. If it finds a power source or is struck by lightning, it enters a positive, supercharged state. While supercharged, an ion slime is faster and much more difficult to catch. An ion slime, with its amorphous form, is unstable and holds a charge for only a handful of seconds. If the ion slime doesn’t find a suitable target before the supercharged state ends, it suffers painful feedback as the electricity grounds out internally, and it returns to its dampened form.

Section 15: Copyright Notice

Tome of Beasts 3 © 2022 Open Design LLC; Authors: Eytan Bernstein, Celeste Conowitch, Benjamin L. Eastman, Robert Fairbanks, Scott Gable, Basheer Ghouse, Richard Green, Jeremy Hochhalter, Jeff Lee, Christopher Lockey, Sarah Madsen, Ben Mcfarland, Jonathan Miley, Kelly Pawlik, Sebastian Rombach, Chelsea Steverson, Brian Suskind, Mike Welham

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