Amphibious. The lurker can breath both air and water.

Environmentally Sensitive Skin. The abyss lurker has advantage on Perception (Wisdom) checks that have to do with smell, touch and hearing. Also, the abyss lurker can sense the location of all Humanoid, Beast, Monstrosity and Plant creatures within 15 ft of it. 

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., 1 target. Hit: 4 (1d4+2) piercing damage. 

Arm Thrust. Melee Weapon Attack: +5 to hit, reach 5 ft., 1 target. Hit: 7 (1d8+2) bludgeoning damage. If the target or the lurker is in an area of obscure light, the abyss lurker has its Strength increased by 1 until the end of the next round. While the lurker's Strength is increased this way, its Strength modifier is added on to its attacks.

Shadow-Powered Stone. RangedWeapon Attack: +5 to hit, range 10/20 ft., 1 target. Hit: 5 (1d6+1) bludgeoning damage and 2 necrotic damage.

Screech (Recharge 5-6). The lurker releases a dreadful screech. All creatures within 20 ft of the lurker must make a DC 15 Wisdom saving throw, taking 8 (2d4) necrotic damage and be frightened for 2 minutes on a failed save, or half as much damage and only be frightened for 1 round on a success.