Avatar of the Dungeon Master

Are You Sure You Want To Do That?  Hostile creatures that start their turn within 120 ft. of the Dungeon Master must succeed at a DC 26 Wisdom saving throw or be frightened of the Dungeon Master. They can repeat the save at the end of each of their turns, ending the effect on a success. While frightened in this way, creatures take 22 (4d10) psychic damage whenever they deal damage to the Dungeon Master.

Legendary Resistance (5/Day). If the Dungeon Master fails a saving throw, they can choose to succeed instead.

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

Mental Gymnastics. The Dungeon Master can concentrate on any number of spells at once, and has advantage on Constitution saving throws to maintain concentration on a spell.

Spellcasting. The Dungeon Master can cast the following spells (DC 26) without verbal or material components:

At will: bless, bane, detect magic, detect thoughts, enhance ability, alter self, gift of gab, dispel magic, sending, dimension door, hallucinatory terrain, greater invisibility (self only), fabricate, creation, dream, scrying, control weather, mind blank (self only), foresight (self only)

3/day each: command (6th level), scatter, phantasmal force, counterspell (6th level), zone of truth, bestow curse, revivify, polymorph, slow, greater restoration, telekinesis, hold monster, etherealness, teleport, earthquake, time stop

1/day each: mass suggestion, reverse gravity, counterspell (9th level), astral projection, meteor swarm, true resurrection, power word stun, shapechange, gate, storm of vengeance, wish

No. The Dungeon Master bends fate, causing one creature (including itself) to reroll a d20. The Dungeon Master chooses which roll to keep.

The Dungeon Master can take 5 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 Dungeon Master regains spent legendary actions at the start of its turn.

Move. The Dungeon Master moves up to its speed without provoking opportunity attacks. 

At-will Spellcasting. The Dungeon Master casts an at-will spell. 

Spellcasting (Costs 2 Actions). The Dungeon Master casts a spell.