Amphibious. The abyssal can breathe air and water.

Crustacean Speech. The abyssal can communicate simple concepts to crabs, lobsters, and other crustaceans or crustacean-like creatures when it speaks Demolith.

Demolith Subtype. The abyssal has the "(demolith)" tag, which has no rules of its own, but is a tag that affects the abyssal in the same way that it would affect a demon or devil.

Semi-Immortal Nature. The abyssal can't die of old age unless affected by magic of a spell of 6th level or higher and doesn't require food, drink, air, or sleep.

Multiattack. The abyssal makes three attacks; two with its trident and one with its tail. Alternatively, it makes one melee attack and two ranged attacks.

Dagger. Melee or Ranged Weapon Attack: +7 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 5 (1d4 + 3) piercing damage plus 4 (1d8) acid damage.

Tail. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) bludgeoning damage.

Forceful Strike. Melee or Ranged Weapon Attack: +6 to hit, reach 5 ft. or range 60 ft., one target. Hit: 9 (1d12 + 3) acid, force, or cold damage (abyssal's choice).

Summon Elemental (3/Day). The abyssal channels powerful sorcerous magic to cause a hellborn water elemental to appear at a point the abyssal can see within 100 feet of it. The summoned elemental acts as an ally of its summoner and can't summon other creatures. It remains for 1 minute, until it or the abyssal dies, or until the abyssal dismisses it as an action.

Spellcasting. The abyssal casts one of the following spells, using Charisma as the spellcasting ability (spell save DC 15, +7 to hit with spell attacks).

At will: ray of frost (2d8), thaumaturgy, mage hand

3/day each: burning hands, fog cloud, grease

2/day: darkness