Acid Mustard Jelly

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Medium Ooze, Neutral

Armor Class 12

Hit Points 75 (10d8+30)

Speed 20 ft.

STR 14 (+2)

DEX 6 (-2)

CON 16 (+3)

INT 1 (-5)

WIS 6 (-2)

CHA 1 (-5)

Saving Throws Con +5

Damage Vulnerabilities fire

Damage Resistances bludgeoning; piercing; slashing

Damage Immunities acid, poison

Condition Immunities charmed, frightened, grappled, paralyzed, petrified, poisoned

Senses blindsight 60 ft.

Languages —

Challenge 4 (1,100 XP) Proficiency Bonus +2

Amorphous. The Acid Mustard Jelly can move through a space as narrow as 1 inch wide without squeezing.

Corrosive Touch. A creature that touches the Acid Mustard Jelly or hits it with a melee attack while within 5 feet of it takes 10 (3d6) acid damage.

Split. When the Acid Mustard Jelly is subjected to slashing or piercing damage, it splits into two new jellies if it has at least 10 hit points remaining.

Actions

Multiattack. The Acid Mustard Jelly makes two pseudopod attacks.

Pseudopod. Melee weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 13 (2d8+4) acid damage. If the target is a creature, it must succeed on a DC 14 Dexterity saving throw or be grappled (escape DC 14). Until the grapple ends, the target is restrained and takes 7 (2d6) acid damage at the start of each of its turns.

Acid Spray (Recharge 5-6). The Acid Mustard Jelly expels a spray of acid in a 15-foot cone. Each creature in that area must make a DC 14 Dexterity saving throw, taking 21 (6d6) acid damage on a failed save, or half as much on a successful one.

Environment Swamp, Underdark

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Lore & Description

Appearance

The Acid Mustard Jelly is a grotesque, amorphous mass of bright yellow goo, radiating a faintly sinister glow. Its surface bubbles and churns, releasing noxious vapors that sting the eyes and throat. The jelly's texture is slimy, and it has a nearly semi-transparent quality, allowing one to see the acidic churning within it.

Behavior & Origins

Acid Mustard Jellies are remnants of failed experiments once conducted by alchemists who sought to harness the properties of mustard gas and acid. They inhabit murky swamps and dark caves, exhibiting aggressive behavior to protect their territory. They are drawn to areas of high humidity and typically dissolve any organic matter they consume, leaving behind only bones and remnants of armor. Those who encounter these jellies are advised against direct contact, as their corrosive touch can quickly degrade flesh.

Generation Info

Original prompt:
"A mustard jelly that burns with acid"

Created: Jan 28, 2026
Modified: May 31, 2026