Monster of the week: Voracious Shriller

This week's creature is another home-brew for my current campaign: the Voracious Shriller, both in young swarming form, or the quite dangerous adult form.
In many ways, it's behavior is akin to the Velociraptor from Jurassic Park, with a twist to it. It's above intelligence (for an animal) and innate Psionic abilities make it quite dangerous for any party wandering the countryside.

"What the hell is happening!?" (A young adventurer caught in the middle of a Voracious Shriller swarm's Cacophony)

Voracious Shriller(swarm)
Large Swarm/ Tiny animal
Armor Class 10
Hit Points 25 (3d10+3)

Speed 30' (6 squares)

Initiative +2

Senses ultra-vision (60')
STR(14/2) DEX (14/2) CON(12/1)
INT(6/-2) WIS(14/2) CHA(8/-1)
Alignment unaligned

Languages basic, animal

Traits

• Swarm Resistance: A swarm has Resistance to all single target damage and has Advantage to all saves due to it's diffuse, overwhelming and chaotic nature. 
• Swarm Vulnerability: A swarm is Vulnerable to any area effect damage and has Disadvantage to all saves against Area Effects.
• Swarm Form: A swarm can squeeze through gaps fitting it's smallest member, usually a tiny creature.
• Swarm Dynamics: When an enemy creature within 5' ends it's turn, the Swarm will gain an immediate Reaction. This action can be one of the following:
• Overcome: Large and smaller creature. The Swarm tries to overcome and topple the creature. Make a STR vs STR context. On failure, the target falls Prone and takes d6+2 damage.
• Disengage: The Swarm tries to move away from the creature. It gains Disengage and must use it instantly.

Actions

• Melee Attack - Hundreds of Teeth: +5 to hit (reach 5', one creature). Hit: 8 (2d4+2) piercing damage. On hit, the target is Hindered (as per Combat Action rule).("The swarm moves onto you, climbing your body, trying to pierce armor and skin with hundreds of razor-sharp teeth!")
• Range Attack - Cacophony (5-6): (Cloud 60', anyone who can hear it, Mind Affecting). Each Creature in range make a WIS save DC12. On failure, it is Deafened and Paralyzed for 1 minute (10 rounds). Make another save at the end of each affected creatures turns. On success, the effect ends and the creature can act normally on it's next turn. ("The deafening shrills from the swarm overwhelms your senses, as if thousands of needles were plunged into your brain at the same time!")

Encounter Building Level (3) Experience (80)
Description

Female adult Voracious Shriller can lay 50-150 (10d20) eggs a year, during which the male (usually smaller and weaker) is killed. These eggs will take about a month to hatch. From then on, the young will behave as one entity, linked together by a collective mindset (Psionic in nature) under the control of the adult female. For about 2 years, they will gain very little mass nor grow much in size.
The swarm will often be left by the female to hunt and feed on it's own though, if the female senses trouble, either directly or via the mind feedback from the swarm, she will order the swarm to retreat to the lair while she goes and deal with it.
After 2 years however, they will gain individual consciousness and a fierce competition will erupt among the young, during which most of them will be killed. The few survivors will then be chased away from the lair by the Female, and repeat the cycle elsewhere, as adults.
Swarms hunting patterns are to stalk, confuse, then ambush their preys. When the attack is decided, it will use it's Cacophony attack (which is actually Psionic; the shrills just adding some effect to it) then move in and try to overwhelm the target as fast as possible.
Environment(rare/1-4)

High grasslands, Dense forests
Behavior 
Chaotic, Territorial, Predator (stalker), Omnivore

Load-Out 
n/a
Treasure

n/a (see Note on Lair)

Voracious Shriller(adult)
Large Animal
Armor Class 14
Hit Points 50 (6d10+6)

Speed 40' (8 squares)

Initiative +4

Senses ultra-vision (60')
STR(16/3) DEX (14/2) CON(16/3)
INT(10/0) WIS(12/1) CHA(8/-1)
Alignment unaligned

Languages basic, animal

Traits

• Shelled Mind: The Voracious Shriller's mind is protected against all mind affecting spells and it receives Advantage on such Saves.
• Cunning Reflexes: The Voracious Shriller's instincts allows him to take a second Action on each of it's turns. This action can only be used to Disengage, Hide or Hustle.
• Mind Invasion: A creature targeted by the Mind Invasion effect is considered as Unconscious in respect to anything happening but the Mind Invasion. At the beginning of each of the target's turns, Make an INT contest check between the Shriller and the target. Whoever wins the contest inflicts d6 + INT modifier between the two as temporary INT damage to the other. Temporary INT is restored after a short rest.
• If the Shriller reaches 0 temporary INT first, the Mind Invasion ends and the Shriller is Stunned until the end of it's next Turn.
• If the Target reaches 0 temporary INT first, it's mind is destroyed and falls into a coma (see note: Coma).
• On a critical failure by either the target or the Shriller, the lost INT is 2d6 + INT modifier instead. 
• On a critical success by the target, Mind Invasion ends immediately and the Shriller is Stunned until the end of it's next Turn.
• If the Shriller suffers Stunned, Charmed, Deafened, Intoxicated, Paralyzed or Unconscious status during a Mind Invasion, the effect automatically ends.

Actions
(When the Voracious Shriller uses the Attack Action, he can choose to make another Bite or Claws Attack as part of the current Action)

• Melee Attack - Bite: +5 to hit (reach 5', one creature). Hit: 10 (2d6+3) piercing damage.("the Shriller tries to bite you!")
• Melee Attack - Claws: +4 to hit (reach 5', one creature). Hit: 8 (d8+3) slashing damage. On hit, make a STR vs STR/DEX (target decides) Contest check. On failure, Target is Prone. ("the Shriller leaps onto you, claws forward!")
• Range Attack - Mind Lash (6): (30', one creature, ignore cover). Make a INT save DC 14. On failure, target is affected by Mind Invasion (see traits). A Voracious Shriller can only maintain one Mind Invasion at a time but can keep attacking normally otherwise.("the Shriller let loose an ear-splitting cry as it's eyes lock with yours for a second, and you feel something entering your mind!")

Encounter Building Level (6) Experience (600)
Description
Voracious Shrillers are large bipedal beasts with disproportionate jaws that open three ways, revealing rows of razor-sharp teeth. They usually have a thick bluish hide that earned them the name of "Sapphire Devils" in some regions.
To the experienced adventurers, they look quite alike the Ethereal Marauders but while they might have a common ancestor, the Shriller and the Marauder only have in common their looks and their intelligence.

Most of the adult Voracious Shrillers are females, the male being very shy and usually dead within a year or two of reaching adulthood. The females are very clever predators, stalking and ambushing preys, sometimes for days, waiting for the correct time.
During combat, it will try to weaken it's prey, rushing in to bite and claw at it, then running away using it's Cunning Reflexes. Against multiple opponents, it will use Mind Lash on the most obviously dangerous one, while focusing it's physical attacks on the apparently weaker ones.
As a note, the Female Voracious Shriller is automatically aware of anything happening to it's infant swarms if within a 5 miles radius.
Shrillers live for about 20 to 30 years but remain quite rare due to their voracious nature and tendency to kill each other.
Environment(rare/1)

High grasslands, Dense forests
Behavior 
Chaotic, Territorial, Predator (stalker), Omnivore, Ultra Aggressive, Intelligent Hunter

Load-Out 
n/a
Treasure

n/a (see Note on Lair)

Note Coma
When in a Comatose state, you are considered as Unconscious and you need others to take care of you, feed you and all that it means.
For each full week in Coma, roll a DC10 INT Check. You awake after 3 successes, critical successes counting for 2, critical failure removing 2 success and normal failure removing 1.
If you go below 0 successes at any point, you die.

• The Spell Lesser Restoration can be used once per day to grant an additional automatic Success.
• The Spell Greater Restoration can be used to immediately leave the comatose state caused by Mind Invasion.

Note Lair

The lair of the Voracious Shriller will usually be a small tunnel system dug up directly under the earth somewhere within it's 10 miles territory. The passages will be about 5' high by 5' wide and quite steep at first, leveling after about 30' and leading into a main chamber around 40' by 40'. 
There will be the eggs or the very young Shrillers and the remains of whoever and whatever the Shriller brought home for dinner.

Quick Plot Hook
The PCs are hired as bodyguards to the local Lord's son during the spring hunting party and after a couple days travelling through the old forest, people start going missing. 
First it was the maid who disappeared without a trace during the night. Then it was the cook who went to collect water from the river and never returned. Then, one night, the hunting party is attacked by swarms of bluish shrilling creatures, leaving barely anyone alive and fit....
A Voracious Shriller recently established it's lair in the local forest and since then, game has been scarce and people have gone missing. Another swarm just hatched recently, bringing the number to four now, and the mommy is on the prowl as well, glad to see so many tasty creatures so close to it's lair.
Hunted, with many injured or comatose, the PCs must bring the lord's son back to safety at all cost, the nearest village being 3 days through thick forest.