Amphibious. The accantus can breathe air and water.

Innate Spellcasting. The accantus's innate spellcasting ability is Charisma (spell save DC 16, +8 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

• At will: shape water, control water, fog cloud
• 3/day each: tidal wave, water breathing, water walk
• 1/day each: conjure elemental (water only), maelstrom

Multiattack. The accantus makes two attacks with its Tainted Trident.

Tainted Trident. Melee or Ranged Weapon Attack: +7 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 13 (2d8 + 4) piercing damage plus 9 (2d8) necrotic damage.

Riptide Grasp (Recharge 5–6). The accantus conjures a swirling vortex of water in a 20-foot radius centered on itself. Each creature of the accantus’s choice within the area must succeed on a DC 16 Strength saving throw or be pulled 15 feet toward the accantus and take 18 (4d8) bludgeoning damage. If a creature is pulled adjacent to the accantus, it is grappled (escape DC 16).

Drown in Despair (Recharge 6). The accantus targets one creature within 30 feet that it can see. The target must succeed on a DC 16 Constitution saving throw or be overwhelmed by a crushing wave of water and emotions. The target takes 27 (6d8) necrotic damage and is stunned until the end of its next turn.

Watery Form. As a bonus action, the accantus can transform its body into a living, flowing form of water for up to 1 minute. While in this form, the accantus has resistance to all damage except lightning and force, can move through a space as narrow as 1 inch wide without squeezing, and can enter a hostile creature's space and stop there. It can revert to its normal form as a bonus action.

Tainted Fury. When the accantus takes damage, it can use its reaction to channel its inner rage. Until the end of its next turn, it gains advantage on all attack rolls, and its melee attacks deal an extra 7 (2d6) necrotic damage. Once the accantus uses this feature, it can’t use it again until it finishes a short or long rest.