Ancient Chronomancer

Spellcasting. The chronomancer is a 9th-level spellcaster. Its spellcasting ability is Intelligence (save DC 14, +6 to hit with spell attacks). The chronomancer has the following wizard spells prepared:
Cantrips (at will): blade ward, light, 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 chronomancer choses 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 16 (3d10) necrotic damage on a failed save, or half as much damage on a successful one.

Slow Projectile. If the chronomancer is targeted by a ranged attack, it can alter the flow of time nearby, causing incoming projectiles to slow down. Until the start of its next turn, the chronomancer has a +10 bonus to AC against ranged attacks.