Blind. Unless a creature makes noise within 60ft of the Secutor, it's considered Hidden.
If Deafened, the Secutor can't take any actions or reactions except Frenzy.

Keen Hearing. The Secutor has advantage on Wisdom (Perception) checks based on hearing.

Sensory Overload. If hit by Thunder damage, or any loud explosion occurs within 5ft of the Secutor, it must make a DC 20 Con Saving throw. On a fail, it's Deafened, Stunned and loses all immunities and resistances for 1 turn.

Vigilant. The Secutor can always use its Targeting reaction, even if a reaction has been used previously in the same turn.

Legendary Resistance. (3/Day).
If the Secutor fails a saving throw, it can choose to succeed instead.

Multiattack. The Secutor makes two Swipe attacks.

Swipe. Melee Attack Roll.
+6 to hit. 7 (1d8 + 4) Slashing damage.

Frenzy. Dex Saving Throw (DC 15).
This action may only be used while Deafened.
The Secutor spins around and moves 15ft in d6 direction, then 15ft in d6 direction, slashing at anything in its way. On a failed save, the targets take 7 (1d8 + 4) Slashing damage and is Maimed for 1 turns. 

Locate. Range 60 ft. The Secutor makes a Wisdom (Perception) check.

Retaliate. Trigger: The Secutor is hit or missed by a melee attack roll.
Response: The Secutor elbows the target, who makes a DC 15 Dex Saving throw. On a fail,  the target takes 8 (1d6 + 4) Bludgeoning damage, is knocked back 5ft and gets the Prone condition.

Targeting. Trigger: Any noise within 60ft of the Secutor, or if hit by a ranged attack. 
Response: The last creature or object making noise or attacking is targeted for the Charge action.

The Secutor can take 3 legendary actions per round & only directly after another creatures turn.

Charge. Dex Saving Throw (DC 15).
The Secutor charges 30ft against the targeted creature or sound source.
On a failed save, any targets in the way take 13 (2d8 + 4) Piercing damage.
If the Secutor runs into a wall, its claws get stuck and it must spend its next action removing them.