Ancient Chronomancer

Spellcasting. The Ancient Chronomancer is a 9th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 14, +6 to hit with spell attacks). The Ancient Chronomancer has following Wizard spells prepared:
Cantrips (at will):  Blade Ward, Mage Hand, Ray of Frost, Prestidigitation 
1st level (4 slots): Detect Magic, Expeditious Retreat, Magic Missile, Shield 

2nd level (3 slots): Hold Person, Misty Step

3rd level (3 slots): Blink, Haste, Slow

4th level (3 slots): Banishment, Dimension Door

5th level (1 slot): Cone of Cold

Unmake. The Ancient Chronomancer chooses one creature it can see within 60 feet of it, causing the target's flesh to rapidly age and decompose. The target must make a DC 14 Constitution saving throw, taking 22 (4d10) necrotic damage on a failed save, or half as much damage on a successful one. 

Rewind. When the Chronomancer or another creature makes an attack roll, saving throw, or ability check, it must remake the roll and use the new result. 

The Ancient Chronomancer 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. He regains spent legendary actions at the start of its turn.

Cantrip (Costs 1 Action) The Ancient Chronomancer casts a cantrip.

Summon Shadow (Costs 2 Actions) The Ancient Chronomancer summons a shadow within 5 feet of the Ancient Chronomancer.

Wrinkle in Time (Costs 3 Actions). A wave of different dimensions splash out from the Chronomancer. Each non-undead creature within 20 feet of the Ancient Chronomancer must make a DC 15 Intelligence saving throw against this magic, taking 21 (6d6) psychic damage on a failed save, or half as much damage on a successful one.