Pescavitus

Celestial Weapons. Its weapon attacks are magical. When it hits with any weapon does extra 2d4 radiant (included below).

Immortal Nature. Doesn't require food drink or sleep

Magic Resistance. Advantage: spell/magic effect saves.

Piscine Curse. When a creature reduces the pescavitus to 0 hp that creature is cursed for 5 days (DC 13 Cha negates). Cursed creature can be detected as a fiend with spells such as detect evil and good. In addition for the duration cursed creature gains only half the benefit of magic that restores hp and gains no benefits from finishing a long rest. A creature that consumes any amount of the flesh of a pescavitus is automatically cursed. Curse can be lifted by a remove curse spell or similar magic.

Water Breathing. Can breathe only underwater.

Slam. Melee Weapon Attack: +5 to hit, 5 ft., one target, 6 (1d6+3) bludgeoning damage + 5 (2d4) radiant.

Air Bubble (Recharge: Short/Long Rest). Creates an air bubble around the heads of any number of creatures that are touching it. A creature that benefits from an air bubble can breathe underwater and gains swim speed of 20' if it doesn't already have a swim speed. The air bubbles hold enough air for 24 hrs of breathing divided by number of breathing creatures that received an air bubble.

Healing Touch (3/Day). Touches another creature. Target magically regains 5 (1d8+1) hp and is freed from any disease poison blindness or deafness.