Ancient City Warden

Awoken. The Warden is summoned when any creature activates a Sculk Shrieker four times. The warning count for Sculk Shriekers is specific to each creature, rather than each Shrieker. This means that the creature can activate four different Shriekers in different locations, and a Warden still emerges after the fourth activation. After summoning, the Warden wanders randomly and moves toward nearby vibrations.

Blind. The Warden is fully dependent on hearing, which is extremely sensitive.

Angry. Whenever a creature within 50 ft of the Warden makes noise, the Warden becomes more agitated towards it and adds 1 to its "anger counter". Likewise, if a creature attacks it, it adds a 2 on a failed attack and 3 on a successful one. This helps determine the target in its next round - the Warden attacks the one it's most angry with (that it can find), rather than the closest one.

Blinding. Whether angered or not, the Warden gives the Blindness effect to all creatures within 20 ft of it for one round every second round.

Detect. At the start of each of the Warden's turns, it listens and sniffs the area around it to find a target; rolls a Wisdom (Perception) check.

Claw. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 2d6 + 7 slashing damage.

Sonic Boom. Ranged Weapon Attack:  range 25/50 ft., one target, DC 20 DEX save (target is pushed 10 ft away from the Warden and takes 5d12+5  thunder damage on a failed save or half as much on a success. Additionally, on a failed save, roll a DC 15 CON save to avoid falling under the Deafened condition until the end of the round).

Back to sleep. If the Warden doesn't find a target for five rounds, it burrows back under ground, dissolving into Sculk.

Opportunity Attack. Whenever a creature that the Warden is angry with moves out of its space by means that would make noise (including walking/running) without taking the Disengage action, it makes a Claw attack.

The Warden can take 3 legendary actions per round, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Warden regains spent legendary actions at the start of its turn.

Claw. The Warden makes a Claw attack.

Sonic Boom. The Warden makes a Sonic Boom attack.