Abyssal Sight. Magical darkness doesn't impede the matron's darkvision.

Amphibious. The abyssal matron can breathe air and water.

Magic Resistance. The abyssal matron has advantage on saving throws against spells and other magical effects.

Vile Damage. The abyssal matron deals an additional 9 (3d6) psychic damage to creatures it has charmed or frightened.

Spellcasting. The abyssal matron can cast the following spells using Charisma as the spellcasting ability (spell save DC 13) and using her Abyssal Trident as an arcane focus.

Cantrips (at will): detect thoughts, suggestion
1/day (# slots): charm person, bestow curse

Multiattack. The abyssal matron makes two melee attacks of her choice or exchanges them for a use of her Spellcasting.

Abyssal Trident. Melee Weapon Attack: +4 to hit, 5 ft., one target. Hit: 7 (1d8 + 3) piercing damage plus 3 (1d6) necrotic damage, and the target must succeed on a DC 13 Constitution saving throw or become stunned until the end of the matron's next turn. 

Tail Smash. Melee Weapon Attack: +4 to hit, 5 ft., one target. Hit: 8 (1d10 + 3) bludgeoning damage plus 5 (1d10) piercing damage and the target must succeed on a DC 13 or be knocked prone. 

Abyssal Scream (1/Day). The abyssal matron lets out a harrowing shout in a 15-foot cone. Each creature in that area must make a DC 12 Constitution saving throw, taking 9 (3d6) thunder damage and becoming frightened for 1 minute on a failed save, or taking half as much damage on a successful save and the target isn't frightened. A frightened creature can repeat their saving throw at the end of each of their turns (save ends).

Abyssal Charm (2/Day). The abyssal matron diverts an attacker's attention elsewhere. When she is attacked, but before she knows if the attack hits or misses, she may force the attacker to make a DC 14 Wisdom saving throw. On a failure, the attacker instead targets a creature of the matrons' choice. On a success, the attack hits the matron.

Siphon Soul:  The abyssal matron sucks the soul of the dead to feed its' hunger for power. Whenever a creature is reduced to 0 hit points, as a reaction the abyssal matron can siphon their life force it hers, regaining up to 6 hit points