Chronomancer

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

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

Spellcasting. The Chronomancer is an 20th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 20, +10 to hit with spell attacks). The Chronomancer can cast disguise self and invisibility at will and has the following wizard spells prepared:

Cantrips (at will): fire bolt, light, mage hand, prestidigitation, shocking grasp

1st level (at will): detect magic, identify, mage armor, magic missile

2nd level (at will): detect thoughts, mirror image, misty step

3rd level (at will): counterspell, fly, lightning bolt, fireball, dispel magic, haste

4th level (3 slots): banishment, fire shield, stoneskin, arcane eye, dimension door, polymorph

5th level (8 slots): cone of cold, scrying, wall of force,planar binding,scrying,wall of force, teleportation circle

6th level (5 slot): globe of invulnerability,chain lightning,disintegrate,true seeing,otilukes freezing sphere

7th level (4 slot): teleport,draconic transformation,finger of death,reverse gravity

8th level (3 slot): clone,dominate monster,mind blank*

9th level (2 slot): time stop, foresight*

*The Chronomancer casts these spells on itself before combat.

Dagger of Ages. Melee Weapon Attack: +10 A spectral dagger springs to existence in the Chronomancers hand and he makes a piercing damage and the target must succeed on a DC 21 Constitution saving throw or immediately age 1d20 years and take 27 (6d8) force damage. A greater restoration spell can restore a creature’s age to normal.

Entombed By Time. The chronomancer conjures an hourglass shaped prison in an attempt to trap a creature within 120 feet. That creature must succeed on a DC 21 Dexterity saving throw or be imprisoned. Sand immediately begins to pour from the top of the hourglass to the bottom, causing the trapped creature to age rapidly. A creature that starts its turn within the hourglass ages 1d20 years. If 30 points of damage are dealt to the glass walls of the hourglass in a single turn, the glass shatters and the hourglass disappears.

 The chronomancer can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature’s turn. The chronomancer regains spent legendary actions at the start of its turn.

Dagger. The chronomancer makes an attack with one of its daggers.

Teleport (Costs 2 Actions). The chronomancer magically teleports, along with any equipment it is wearing or carrying, up to 120 feet to an unoccupied space it can see.

Entomb (Costs 3 Actions). The chronomancer uses its Entombed By Time ability.

Rewind Time; When the Chronomancer is reduced to 25% of his maximum Hit points he triggers his rewind time ability. This forces all creatures the Chronomancer chooses within a 5 mile radius to succeed on a DC45 Intelligence or Constitution saving through or be rewound to a point in time the Chronomancer chooses within the last 24 hours. Any creature that succeeds on this saving throw is unaffected by this ability and is immune to its effects for 1 year.

When a creature is affected by this ability they have their hit points, spell slots, and position reset to the point they were at when the effect triggered. If they succeed on the save they are not affected and do not regain hit points or spell slots. 

If no creatures save against the spell DC then the Chronomancer regains all missing hit points and spell slots expended but retains his knowledge of the time that has past. No actions against the Chronomancer in the next immediate round of combat can have advantage against the Chronomancer. Subsequent triggering of this ability have its DC reduced. DC 25 on the second casting, DC 15 on the third, and the ability automatically fails if it triggers a 4th time in less than 1 day. 

On the second casting of this ability all attacks against the Chronomancer in the next immediate round of combat are made at disadvantage. On the third casting of this ability all attack rolls against the Chronomancer automatically fail.

When a creature succeeds against the DC of the spell and does not rewind it prevents the Chronomancer from regaining some of its hit points and spell slots. For each creature that succeeds the Chronomancer looses 1 rank of his highest level spell slots available and 25 maximum hit points.