Ever Burning Soul. Whenever the zvikzer is subjected to fire damage, it takes no damage and instead regains a number of hit points to the equal to the fire damage dealt.

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

Ignited Touch. Everytime the zvikzer hits a creature with a melee attack, the creature takes 11 (2d10) fire damage. This does not trigger the zvikzer's Ever Burning Soul.

Multiattack. The zvikzer makes two attacks with its fists.

Fist. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 22 (4d6 + 8) bludgeoning damage.

Tail. Melee Weapon Attack: +13 to hit, reach 15 ft., one target. Hit: 21 (3d8 + 8) bludgeoning damage. 

Fire Breath (Recharge 5-6).  The Zvikzer exhales fire in a 50-foot cone.  Each creature in that area must make a DC 18 Dexterity saving throw, taking 63 (14d8) fire damage on a failed save, or half as much damage on a successful one.

Summon Lesser Demons (3/Day) The zvikzer casts Summon Lesser Demons without components. 

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

Tail Attack. The zvikzer  makes a tail attack.

Demon Eyes. The zvikzer chooses a creature  that is within 60 ft. of the zvikzer. The creature needs to roll a wisdom saving throw against the zvikzer's Intimidation roll. If the zvikzer's win, the creature gets frightened until the end of that creature's turn.

Lava Swirls. (Cost 3 Actions) The zvikzer get surrounded by swirling lava. Every creature within 10 ft. of the zvikzer must succeed on a DC 20 Dextarity saving throw or take 18 (4d8) fire damage. The Swirl stays around the zvikzer until the start of the zvikzer's turn. Anytime someone enters or end their turn in the space of the swirl, they need to reroll their Dextarity saving throw.