Cherufe

Magma Skin. All creatures that start their turn or step into a 5 foot radius of the cherufe take 6 (1d10) fire damage.

Regeneration. The cherufe regains 10 hit points at the start of its turn. If it takes at least 20 hit points of cold damage or is sprayed with at least 5 gallons of water, this trait doesn't function at the start of the cherufe's next turn. The cherufe dies only if it starts its turn with 0 hit points and doesn't regenerate.

Water Susceptibility. For every 5 feet the cherufe moves in water that's a foot or more deep, or if sprayed with more than 5 gallons of water, it takes 2 (1d4) cold damage. If the cherufe starts its turn in water that is 1 foot or more deep, it takes 4 (1d6) cold damage. The damage caused by this trait is not affected by the cherufe's resistance to cold damage. 

Innate Spellcasting. The cherufe's innate spellcasting ability is Charisma (spell save DC 20, +12 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: hellish rebuke, fireball

3/day each: flame strike, immolation

1/day each: incendiary cloud

Multiattack. The cherufe makes three attacks; one magma spit attack, and two claw or tail attacks.

Claw. Melee Weapon Attack: +15 to hit, reach  5 ft., one target. Hit: 15 (2d6 + 8) slashing damage. 

Tail. Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit:  18 (2d8 + 8) bludgeoning damage.

Magma Spit. Ranged Weapon Attack: +15 to hit, range 20/60 ft., 1 target. Hit: 21 (2d12 + 8) fire damage. When hit, the target must make a (DC 23) DEX saving throw, on a failed save that creature catches fire. Until someone takes an action to douse the fire, that creature takes 6 (1d10) fire damage at the start of each of its turns.

The cherufe can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The dragon regains spent legendary actions at the start of its turn.

Tail Attack. The cherufe makes a tail attack.

Magma Pool (Costs 2 Actions). The cherufe makes a magma pool under its feet in a 5 foot radius. All creatures that start their turn in or enter the area of the pool takes 12 (2d10) fire damage and catch on fire. Until someone takes an action to douse the fire, that creature takes 6 (1d10) fire damage at the start of each of its turns. While an on fire creature is in the magma pool, the fire cannot be doused.

Cast a Spell (Costs 3 Actions). The cherufe uses spellcasting.