n medium aberration 

Perception +15; darkvision

Languages Aklo

Skills Acrobatics +12, Athletics +13

Str +2 Dex +3 Con +4 Int -3 Wis +3 Cha +0

AC  21; All-Around Vision; Fort +15, Ref +12, Will +10

HP 120; Weaknesses bludgeoning 5

Gibbering (auditory, aura, emotion, enchantment, incapacitation, mental, occult) Each creature that begins its turn within 60 feet of a gibbering mouther must attempt a DC 19 Will save. On a failure, they are confused for 1 round. On a success, they are temporarily immune for 1 minute.

All-Around Vision

Reactive Gnaw [R] Trigger An adjacent creature deals the gibbering mouther slashing damage. Effect The gibbering mouther's wound opens into another maw. It makes a jaws Strike against the triggering creature.

Speed 10 feet, swim 20 feet

Melee [>] jaws +14 (finesse), Damage 2d8+5 piercing plus 1d4 persistent bleed damage and Grab

Ranged [>] spittle +14 (range 30 feet), Damage 4d6 acid and burn eyes

Burn Eyes A creature that takes damage from a gibbering mouther's spittle must succeed at a DC 22 Fortitude save or be dazzled for 1 round (or blinded for 1 round on a critical failure).

Engulf [>] DC 22, 3d8 piercing, Escape DC 22, Rupture 8.

Ground Manipulation [>>] (occult, transmutation) The gibbering mouther causes stone and earth under its body to grow soft and muddy, remaining so for 1 minute after the mouther moves off the location. A gibbering mouther can move through these areas with ease, but other creatures treat them as difficult terrain.

Bestiary, page 176.