Aillén Mac Midgna, the Muse of Cinders

Fey Ancestry. The fey has advantage on saving throws against being charmed, and magic can’t put the drow to sleep.

 Hypnotic Charm. The fey emanates a marvelous song that echoes out to a reach of 60 feet. The charm causes all humanoids to fall in a state of awe and loss. Each creature in the area who hears the song must make a Wisdom saving throw. On a failed save, the creature becomes charmed for the duration. While charmed by this charm, the creature is incapacitated and has a speed of 0. The charm ends for an affected creature if it takes any damage or if someone else uses an action to shake the creature out of its stupor. Fey creatures of CR 16 or lower that can hear this song lose their immunity to the charmed effect.

Legendary Resistance (3/Day). If the fey fails a saving throw, it can choose to succeed instead.

 Multiattack. The fey makes two ignite attacks.

Ignite. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 20 (2d12 + 7) fire damage. If the target is a creature or a flammable object, it ignites. Until a creature takes an action to douse the fire, the target takes 6 (1d12) fire damage at the start of each of its turns.

Fire Breath (Recharge 5-6). The fey exhales fire in an 90-foot line that is 5 feet wide. Each creature in that line must make a DC 20 Dexterity saving throw, taking 66 (12d10) fire damage on a failed save, or half as much damage on a successful one. On a failed save, the creature also ignites. Until a creature takes an action to douse the fire, the target takes 6 (1d12) fire damage at the start of each of its turns. Creatures immune to fire damage instead have resistance when damaged by this attack. 

The fey 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 fey regains spent legendary actions at the start of its turn.

Attack. The fey uses its ignite attack.

Fly. The fey flies at double speed, ignoring attacks of opportunity.

Song of Fire & Ash (Costs 2 Actions). Each creature in a 20-foot-radius sphere centered on the fey must make a Dexterity saving throw. A target takes 35 (10d6) fire damage on a failed save, or half as much damage on a successful one.