Water Devil

Devil's Sight. Magical darkness doesn't impede the devil's darkvision. 

Magic Resistance. The devil has advantage on saving throws against spells and other magical effects. 

Amphibious. The devil can breathe both air and water. 

Innate Spellcasting. The devil's spellcasting ability is Charisma(Save DC 14, +6 to hit with spells). The devil can innately cast the following spells, requiring no material components:

• At will: Shape water, Create or Destroy water. 
• 3/day each: Fog cloud, Ice knife, Invisibility. 
• 1/day each: Fear, Tidal wave, Wall of water. 

Multiattack: The Water Devil makes 2 attacks, one with its Bite and one with its Claws. While submerged in liquid, it can make a Tail attack. It can replace any of these actions with Water Breath. 

Bite: Melee weapon attack, +7 to hit, reach 5ft, one target. Hit 8(1d8+4) piercing damage plus 9(2d8) cold damage. 

Claws: Melee weapon attack, +7 to hit, reach 5ft, one target. Hit 11(2d6+4) slashing damage. 

Tail: Melee weapon attack, +7 to hit, reach 15ft, one target. Hit 15(2d10+4) bludgeoning damage. 

Water Breath(Recharge 5-6): The Water Devil releases a torrent of water in a 20ft line that is 5ft wide. Each creature in that line must make a DC 14 Strength saving throw. On a failed save, a creature takes 14(4d6) bludgeoning damage and, if the creature is large or smaller, it is pushed 10ft backward and is knocked prone. On a success, a creature takes half as much damage and isn't pushed away or knocked prone.