Sinuous Dexterity. The Aberrant Screecher has advantage against being grappled, restrained, and knocked prone

Multiattack. The Aberrant Screecher can make 2 claw attacks as a single action. 

Claw. Melee Weapon Attack: + 8 to hit, reach 10 ft., one target. Hit: 2d4 Slashing damage and 1d6 Necrotic Damage. 

Psychic Scream. The Aberrant Screecher lets out a powerful scream that can be heard from a mile away. Any creature within 60ft of the Screecher must succeed a DC 16 Wisdom Saving Throw or take 3d10 Psychic Damage and become frightened for the next minute. On a creatures turn they may use an action to attempt the Saving throw again to remove the frightened condition

Perish Wail. The Aberrant Screecher lifts a grappled creature close to it's face and lets out a powerful wail. The target must make a DC 16 Constitution saving throw. On a failed saving throw the target falls unconscious, on a success the target is petrified for 1 minute.  

Flailing Leap. As a Bonus Action the Aberrant Screecher may jump 20ft to an open position in range. Each creature engaged with the Aberrant Screecher and creatures within 5ft of the jumps destination, must succeed a DC 16 Strength saving throw or be knocked prone. 

Furious Assault. The Aberrant Screecher takes an additional attack action. 

Pained Howl. When the Aberrant Screecher receives damage of any type it may use its reaction to let out a painful wail. Every creature within 20ft must make a DC 16 Constitution Saving Throw or be Stunned until the end of their next turn.

Opportunity Grapple. The Aberrant Screecher can use the Grapple action as it's attack of Opportunity