Bitxohr Demon

Legendary Resistance (1/Day).  If the demon fails a saving throw, it can choose to succeed instead. 
Magic Resistance.  The demon has advantage on saving throws against spells and other magical effects. 
Magic Weapons.  The demon's weapon attacks are magical. 
Power Aura.  At the start of each of the demon's turns, each creature within 5 feet of it takes 3 (1d6) fire damage and 3 (1d6) lightning damage.  A creature that touches the demon or hits it with a melee attack while within 5 feet of it takes 3 (1d6) fire damage and 3 (1d6) lightning damage. 

Multiattack.  The demon can use its Frightful Presence.  It then makes two attacks: one with its bite and one with its claws. 
Bite.  Melee Weapon Attack: +9 to hit, reach 5 ft., one target.  Hit: 11 (2d6 + 4) piercing damage plus 7 (2d6) fire damage. 
Claw.  Melee Weapon Attack: +9 to hit, reach 5 ft., one target.  Hit: 9 (2d4 + 4) slashing damage plus 5 (2d4) lightning damage.  
Tail.  Melee Weapon Attack: +9 to hit, reach 5 ft., one target.  Hit: 6 (1d4 + 4) bludgeoning damage and 2 (1d4) thunder damage. 
Frightful Presence.  Each creature of the demon's choice that is within 60 feet of the demon and able to see and hear it must succeed on a DC 16 Wisdom saving throw or become frightened for 1 minute.  A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.  If a creature's saving throw is successful or the effect ends for it, the creature is immune to the demon's Frightful Presence for the next 24 hours. 
Power Breath (Recharge 5–6).  The demon exhales energy in a 25-foot cone.  Each creature in that area must make a DC 16 Dexterity saving throw, taking 21 (6d6) fire damage, 14 (4d6) lightning damage, 7 (2d6) thunder damage, and 7 (2d6) force damage on a failed save, or half as much damage on a successful one. 
Invisibility (3/Day).  The demon magically turns invisible until it attacks or until its concentration ends (as if concentrating on a spell).  Any equipment the demon wears or carries is invisible with it. 

The demon 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 demon regains spent legendary actions at the start of its turn. 
Tail Attack.  The demon makes a tail attack. 
Injury to Insult.  Each creature frightened of the demon takes 7 (2d6) psychic damage. 
Wing Attack (Costs 2 Actions).  The demon beats its wings.  Each creature within 5 feet of the demon must succeed on a DC 17 Dexterity saving throw or take 11 (2d6 + 4) thunder damage and be knocked prone.  The demon can then fly up to half its flying speed.