Aquamoris

Water Core. The aquamoris is resistant to piercing damage.

Elemental Death. The aquamoris is resistant to necrotic damage. Anyone of any good alignment must succeed a DC 12 Constitution saving throw if they are within 5 feet of the aquamoris, or take 1d4 necrotic damage every round. They are able to make the save at the start of their next turn. If they succeed the save, they become immune to it's seeping darkness for the next hour.

Multiattack. The aquamoris makes two attacks; one claw and one tail. Or it can use both of its attacks to use its breath weapon.

Claw. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (1d8 + 4) slashing damage.

Tail. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 4) bludgeoning damage.

Fire Breath. The aquamoris exhales black fire in a 15-foot cone. Each creature in that area must make a DC 18 Dexterity saving throw, taking 10 (2d10) fire damage and 4 (2d4) necrotic damage on a failed save, or half as much damage on a successful one.

Flaming Ice. If the aquamoris takes cold or fire damage, it can return the damage rolled by half within a 10ft radius of itself.