Abyssal Ambusher. In the first round of combat, the Abyssal Eye has advantage on attack rolls against any creature it has surprised.

Water Breathing. The Abyssal Eye can breathe only underwater.

Multiattack. The Abyssal Eye makes two attacks with its Bite.

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., 1 target. Hit: 13 (2d8 + 3) piercing damage. 

Suction Shot. RangedWeapon Attack: +4 to hit, range 30/60 ft., 1 target. Hit: The target is grappled (escape DC 14), and if it is Medium or smaller, it is pulled up to 20 feet straight toward the Abyssal Eye.

Abyssal Gaze (Recharge 5–6). The Abyssal Eye releases a haunting, luminescent glow from its large eyes, targeting one creature it can see within 60 feet of it. The target must succeed on a DC 14 Wisdom saving throw or be frightened for 1 minute. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the Abyssal Gaze for the next 24 hours.

Ink Cloud (1/Day). When the Abyssal Eye takes damage, it can expel an ink cloud in a 20-foot radius around it. The cloud spreads around corners, and that area is heavily obscured to creatures other than the Abyssal Eye. Each creature in the area other than the Abyssal Eye must succeed on a DC 14 Constitution saving throw or be poisoned until the end of the creature's next turn. The cloud dissipates after 1 minute, and the Abyssal Eye can't use this reaction again until it takes a short or long rest.