Marsh Jelly

Medium aberration, unaligned

Armor Class 13
Hit Points 58 (9d8 + 18)
Speed 5 ft., fly 30 ft. (hover)

10 (+0) 17 (+3) 14 (+2) 3 (-4) 12 (+1) 11 (+0)

Skills Perception +3, Stealth +5
Condition Immunities blinded, prone
Senses darkvision 60 ft., passive Perception 13
Challenge 3 (700 XP)

Special Traits

  • Death Burst. When the marsh jelly dies, its body bursts in a spray of acid and protoplasm. Each creature within 10 feet of it must make a DC 13 Dexterity saving throw, taking 10 (3d6) acid damage on a failed save, or half as much damage on a successful one.
  • Keen Smell. The marsh jelly has advantage on Wisdom (Perception) checks that rely on smell.


  • Multiattack. The marsh jelly makes two Tentacle attacks.
  • Tentacle. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) bludgeoning damage plus 3 (1d6) poison damage.
  • Paralyzing Sting (recharge 5-6). The marsh jelly makes a tentacle attack. If the attack hits, the target takes an extra 7 (2d6) poison damage and must succeed on a DC 12 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.


  • Disorienting Glow. When a creature the marsh jelly can see hits it with an attack, the marsh jelly’s body glows and dims rapidly, disorienting creatures within 5 feet of the marsh jelly. Each creature in that area must succeed on a DC 12 Constitution saving throw or be blinded until the end of its next turn.


This bizarre creature floats slowly through the gloom of swamps and marshes. It has a gelatinous body reminiscent of a jellyfish that is nearly translucent, its four stringy tentacles dangling beneath it in a constant hunt for food. Marsh jellies are roughly man-sized and tend to thrive on giant swamp rats, and other creatures smaller than itself. It is not uncommon however for a marsh jelly or a globe of such creatures to prey on unwary travelers who stray to deeply into open marshland. Marsh jellies are responsible for the strange disappearance of many who enter their swamps for they digest their prey, bones and all, leaving only acid resistant precious metals such as gold behind.

A marsh jelly looks like a hovering, flying jellyfish with a translucent sickly green body and four long dangling grayish-pink tentacles. Many smaller tentacles ring its body and aid the creature in locomotion as well as detecting scents in the air. A marsh jelly’s body emits a pulsating glow when it is threatened or damaged, and the creature can likewise use this glow to lure prey closer to it.

Marsh jellies descend on their prey from above, stinging repeatedly with their venomous tentacles. When wounded, their translucent flesh begins to pulse rapidly with a flashing green strobe effect that tends to disorient its prey, and any other creatures who may seek to harm it.

Section 15: Copyright Notice

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

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