Amphibious.

The marid can breathe air and water.

Elemental Demise.

If the marid dies, its body disintegrates into a burst of water and foam, leaving behind only equipment the marid was wearing or carrying.

Innate Spellcasting.

The marid'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: create or destroy water, detect evil and good, detect magic, fog cloud, purify food and drink
3/day each: tongues, water breathing, water walk
1/day each: conjure elemental (water elemental only), control water, gaseous form, invisibility, plane shift

Actions

Multiattack.

The marid makes two trident attacks.

Trident.

Melee or Ranged Weapon Attack: +10 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 13 (2d6 + 6) piercing damage, or 15 (2d8 + 6) piercing damage if used with two hands to make a melee attack.

Water Jet.

The marid magically shoots water in a 60-foot line that is 5 feet wide. Each creature in that line must make a DC 16 Dexterity saving throw. On a failure, a target takes 21 (6d6) bludgeoning damage and, if it is Huge or smaller, is pushed up to 20 feet away from the marid and knocked prone. On a success, a target takes half the bludgeoning damage, but is neither pushed nor knocked prone.

Marid