From Pathfinder Bestiary 3, which isn't enabled.

Feral Skull Swarm

CREATURE 12

UNCOMMON HUGE EVIL MINDLESS SWARM UNDEAD UNHOLY

Some skull swarms are crafted from the heads of feral and dangerous beasts. These can include predatory cats, bears, dinosaurs, and the like, but just as often they're made from bulls, horses, apes, and other creatures that were gentler in life. In death, a feral skull swarm is bloodthirsty regardless of its origins, with a keen scent for living flesh. Even herbivore skulls diligently chew on the flesh of their swarm's victims.

A skull swarm is composed of reanimated masses of craniums and jawbones, forming a terrifying avalanche of undead fury. Most skull swarms are mindless, though some retain a vestige of wit, awareness, and even magical talents from life, culminating in a highly intelligent swarm mind.

Perception +21; darkvision, scent (imprecise) 30 feet

Skills Acrobatics +22, Survival +21

Str +0, Dex +4, Con +7, Int -5, Wis +3, Cha +4

Feral Trackers

A feral skull swarm gains a +2 circumstance bonus to Perception checks to Seek and to Survival checks to Track, both against any creature that has taken damage from the swarm's Feral Gnaw within the previous 24 hours.

AC 32; Fort +25, Ref +22, Will +19

HP 160, void healing; Immunities bleed, death effects, disease, paralyzed, poison, precision, unconscious; Weaknesses area damage 10, splash damage 10; Resistances bludgeoning 5, cold 10, electricity 10, fire 10, piercing 10, slashing 10

Boneshard Burst

When a feral skull swarm is reduced to 0 Hit Points, it erupts in an explosion of foul energy and bone fragments in a 30-foot burst, dealing 3d12 piercing damage and 2d12 void damage (DC 32 basic Reflex save).

Void Healing

A creature with void healing draws health from void energy rather than vitality energy. It is damaged by vitality damage and is not healed by vitality healing effects. It does not take void damage, and it is healed by void effects that heal undead.

Speed 40 feet

Feral Gnaw

Each enemy in the swarm's space takes 2d6 bludgeoning damage, 2d6 piercing damage, and 2d6 slashing damage (DC 32 basic Reflex save).

A creature that fails its saving throw also takes 1d10 bleed.

Frightening Howl (auditory, emotion, fear, mental)

The feral skull swarm emits a terrifying howl. Each creature within 60 feet must succeed at a DC 32 Will save or become Frightened 2 (Frightened 3 and Fleeing for 1 round on a critical failure).

Whether it succeeds or fails its save, a creature is temporarily immune to Frightening Howl for 24 hours.

Pathfinder Bestiary 3OGL