Huge. The Acklay's space is 20 ft by 20 ft, it has advantage on Strength (Athletics) checks versus large or smaller creatures.

Multiattack. The Acklay makes two Pincer attacks, and two Leg Sweep attacks. It can choose to replace two of these attacks with one mind blast attack.

Pincer. Melee Weapon Attack: +5 to hit, reach 10 ft., one target. Hit: 9 (2d6 + 3) bludgeoning damage. If the target is a Large or smaller creature, it is grappled (escape DC 15). Until this grapple ends, the Acklay can 'pincer' only the grappled creature and has advantage on attack rolls to do so. It can have up to two creatures grappled in this way.

Leg Swat.Melee Weapon Attack:  +5 to hit, reach 10 ft., one target. Hit: (2d6+3) bludgeoning damage. If the target is Large or smaller, it must succeed on a DC 12 Strength Check or be batted 10 feet away and be set as prone .

Multiattack. The Acklay makes 2 Pincer attacks, and 2 Leg Sweep attacks every round.
 It may use Mind Blast In place of one of the 4 attacks if it chooses to do so.

Mind Blast (Recharge 6). The Aberrant Acklay "stares down" one target, emitting psychic energy. A creature of the Aberrant Acklay's choice within 80 feet of it must succeed on a DC 18 Intelligence saving throw or take 25 (3d10 + 10) psychic damage and be stunned for 1 minute. A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If you succeed on the initial saving throw, then nothing happens.