Xanathas Herr der Schatten (Avatar)

Shapechanger. If Xanathas isn't in sunlight or running water, he can use his action to polymorph into a Tiny bat or a Medium cloud of mist, or back into its true form.

While in bat form, Xanathas can't speak, its walking speed is 5 feet, and he has a flying speed of 30 feet. his statistics, other than his size and speed, are unchanged. Anything he is wearing transforms with him, but nothing he is carrying does. he reverts to his true form if he dies.

While in mist form, Xanathas can't take any actions, speak, or manipulate objects. he is weightless, has a flying speed of 20 feet, can hover, and can enter a hostile creature's space and stop there. In addition, if air can pass through a space, the mist can do so without squeezing, and it can’t pass through water. he has advantage on Strength, Dexterity, and Constitution saving throws, and he is immune to all nonmagical damage, except the damage it takes from sunlight.

Legendary Resistance (3/Day). If Xanathas fails a saving throw, he can choose to succeed instead.

Misty Escape. When he drops to 0 hit points outside his resting place, Xanathas transforms into a cloud of mist (as in the Shapechanger trait) instead of falling unconscious.

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

Spellcasting. Xanathas is a 9th-level spellcaster. his spellcasting ability is Intelligence (spell save DC 16, +8 to hit with spell attacks). Xanathas has the following wizard spells prepared:

Cantrips (at will): mage hand, prestidigitation, ray of frost

1st level (4 slots): comprehend languages, fog cloud, sleep, magic missile

2nd level (4 slots): detect thoughts, gust of wind, mirror image, misty step, darkness

3rd level (4 slots): lightning bolt, bestow curse, counterspell

4th level (4 slots): blight, polymorph, phantasmal killer

5th level (4 slot): dominate person, cone of cold, destructive wave

8th level (1 slots): power word stun

Multiattack.  Xanathas makes two attacks, only one of which can be Charm.

Shadow Strike. Melee Weapon Attack: +9 to hit, reach 5 ft., one creature. Hit: 8 (2d8 + 4) bludgeoning damage.

Charm. Xanathas targets one humanoid it can see within 30 feet of him. If the target can see Xanathas, the target must succeed on a DC 17 Wisdom saving throw against this magic or be charmed by him. The charmed target regards Xanathas as a trusted friend to be heeded and protected. Although the target isn't under Xanathas control, it takes his requests or actions in the most favorable way it can.

Each time Xanathas or the Xanathas companions do anything harmful to the target, it can repeat the saving throw, ending the effect on itself on a success. Otherwise, the effect lasts 24 hours or until Xanathas is destroyed, is on a different plane of existence than the target, or takes a bonus action to end the effect.

Children of the Night (1/Day). Xanathas magically calls 2d4 shadow . The called creatures arrive in 1d4 rounds, acting as allies of Xanathas and obeying its spoken commands. The beasts remain for 1 hour, until Xanathas dies, or until Xanathas dismisses them as a bonus action.

Xanathas 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. Xanathas regains spent legendary actions at the start of his turn.

Shadow Defense (Costs 2 Actions). Xanathas draws nearby shadow to him to increase his armour class to 21, this effect drops at the start of his next turn.

Shadow Health (Costs 2 Action). Xanathas absorbs some of the local shadows to regenerate 20hp.

Wave of pure Shadow (Costs 3 Actions). Xanathas surges with purple energy before releasing it as a wave of either Necrotic gas or Psychic energy. Any target in a 30ft radius of him must make a DC 17 Wisdom saving throw or take 20 points of the selected damage type.