Gibbering Mouther
Medium Aberration, neutral
450 XP
Special Abilities
Aberrant Ground
The ground in a 10-foot radius around the mouther is doughlike difficult terrain. Each creature that starts its turn in that area must succeed on a DC 10 Strength saving throw or have its speed reduced to 0 until the start of its next turn.
Gibbering
The mouther babbles incoherently while it can see any creature and isn't incapacitated. Each creature that starts its turn within 20 feet of the mouther and can hear the gibbering must succeed on a DC 10 Wisdom saving throw. On a failure, the creature can't take reactions until the start of its next turn and rolls a d8 to determine what it does during its turn. On a 1 to 4, the creature does nothing. On a 5 or 6, the creature takes no action or bonus action and uses all its movement to move in a randomly determined direction. On a 7 or 8, the creature makes a melee attack against a randomly determined creature within its reach or does nothing if it can't make such an attack.
Actions
Multiattack
The gibbering mouther makes one bite attack and, if it can, uses its Blinding Spittle.
Bites
Melee Weapon Attack: +2 to hit, reach 5 ft., one creature. Hit: 17 (5d6) piercing damage. If the target is Medium or smaller, it must succeed on a DC 10 Strength saving throw or be knocked prone. If the target is killed by this damage, it is absorbed into the mouther.
Blinding Spittle (Recharge 5-6)
The mouther spits a chemical glob at a point it can see within 15 feet of it. The glob explodes in a blinding flash of light on impact. Each creature within 5 feet of the flash must succeed on a DC 13 Dexterity saving throw or be blinded until the end of the mouther's next turn.
Quick Reference
Running This Encounter
The Gibbering Mouther is a chaotic, unpredictable aberration that rewards creative encounters over straightforward combat. Its low AC and relatively modest HP make it vulnerable, but its ability to blind creatures and force saves creates dangerous complications. Use terrain with obstacles and multiple levels to make its slow speed less of a liability, and consider combining it with other creatures that benefit from the confusion it creates. The constant stream of nonsensical gibbering and alien behavior should inform your roleplay to make this a memorably unsettling encounter.
Combat Tactics
The Mouther prioritizes using its Blinding Spittle to incapacitate enemies from range, forcing DEX saves before closing in with its multiple bite attacks. It will chase down isolated or weakened creatures, using its Gibbering ability to distract and disorient groups. The creature fights erratically and without strategy—it attacks whatever is nearest, making it dangerous but predictable once engaged.
Environment & Setting
Ideal in underground caverns, sewers, or aberrant lairs where its aquatic movement offers escape routes and its low light vision provides advantage. Damp, cramped spaces with rough terrain and pools work well to slow melee combatants while giving the Mouther room to maneuver.