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

Legendary Resistance (2/Day). If the avatar fails a saving throw, it can choose to succeed instead.

Stretch Time (Recharge 5-6). The avatar stretches time, giving it another action on his turn.

Spellcasting. The avatar is a 17th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 19, +10 to hit with spell attacks). The avatar has the following spells prepared:
Cantrips (at will): true strike

3rd level (3 slots): haste

9th level (1 slot): time stop

Multiattack. The avatar makes two crush attacks.

Crush. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 19 (3d8 + 6) bludgeoning damage. 

Slow Time. The avatar slows down time for everyone within 30 feet of it. An affected creature's speed is halved, it can't use reactions, and it can take an action or a bonus action on its turn, but not both.

Time Blast (Recharge 6). The avatar targets one creature. That creature must succeed on a DC 17 Wisdom saving throw, or take 2d10 force damage and have time reversed, turning it into a baby for one round. While the creature is a baby, it is unable to act on its turn.

Slow Projectile. The avatar slows down one projectile it can see, reducing its damage when it hits by 2d6.