Monster I’d Like to Fight: Jethrish

Jethrish are enormous jellyfish-like Aberrations with numerous tentacles and a single eye that glows like a dull sun. It is most often found on the edges of the Ethereal plane where it can peer into the Material plane in search of food. Jethrish look for creatures that are isolated and most vulnerable. It will find a place to ambush the creature and quietly phase into the Material plane, laying in wait for its prey to wander by.

Jethrish are well adapted to both the Ethereal and Material planes and have developed the ability to shift creatures and objects between both planes. Permanently shifting a creature or object takes time, but the jethrish can perform momentary shifts in the heat of battle.

One-Eyed Ostaph

A particularly aberrant jethrish is One-Eyed Ostaph, an unusually intelligent and cunning creature. Ostaph is more adept at phasing themselves and objects between the Ethereal and Material planes. Unlike their standard counterparts, Ostaph is more interested in theft. They’ve been known to sneak up on an unsuspecting mark to relieve them of their belongings and quickly return to the Ethereal plane. Ostaph is rumored to have amassed such a hoard of stolen goods that it would make a dragon jealous.

Jethrish

Huge Aberration, Unaligned

Armor Class 15

Hit Points 189 (18d12 + 72)

Speed 0 ft., fly 40 ft. (hover)

STR	DEX	CON	INT	WIS	CHA
23 (+6)	13 (+1)	19 (+4)	6 (-2)	17 (+3)	1 (-5)

Saving Throws Wis +7

Skills Perception +7, Stealth +5

Damage Resistances bludgeoning, piercing, and slashing from nonmagical attacks

Condition Immunities deafened, prone

Senses darkvision 120 ft., passive Perception 17

Languages —

Challenge 12 (8,400 XP)

Proficiency Bonus +4

Severe Injury. If the jethrish is reduced to 100 hit points or less, Blinding Eye doesn’t function until it finishes a long rest.

Actions

Multiattack. The jethrish makes three Displacing Tentacle attacks.

Displacing Tentacle. Melee Weapon Attack: +10 to hit, reach 15 ft., one target. Hit: 20 (4d6 + 6) bludgeoning damage. If the target is a creature, the jethrish uses one of the following options (choose one or roll a d6):

1–2: Disarm. The target must succeed on a DC 17 Dexterity saving throw or objects its holding momentarily become ethereal, causing them to fall to the ground.
3–4: Sunder. The target must succeed on a DC 17 Dexterity saving throw or part of its armor momentarily become ethereal, causing it to fall to the ground. The target’s AC is reduced by 2 until they can re-don their armor. This effect is cumulative. If this reduction causes the target’s AC to be less than their unarmored AC, the target uses their unarmored AC instead.
5–6: Shunt. The target must succeed on a DC 17 Wisdom saving throw or begin to phase in and out of the Ethereal plane until the end of its turn. While phasing, the target’s speed is halved and it can’t take reactions. On its turn, it can use either an action or a bonus action, not both.

Blinding Eye (Recharge 5–6). The jethrish emits a blast of bright light in a 60-foot cone. Each creature in that area must make a DC 17 Constitution saving throw. On a failed save, the creature takes 33 (6d10) radiant damage, and is blinded for 1 minute. On a successful save, the creature takes half as much damage with no additional effects. A blinded target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.