Chronomancer

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

Stretch Time (Recharge 5-6). The chronomancer can take on additional action on its turn. This does not include his multiattack special.

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

ChronoShielding. Physical attacks, including ranged, have disadvantage when attacking the chronomancer. This can be negated if his final concentration is broken. If he looses this, he looses 2 AC until he regains his Temporal Concentration.
Lore: This is due to a special timewarping shielding around him at all time.

Temporal Concentration. The chronomancer has 3 levels of concentration:
First Level. normal concentration, which he can recover from. He has +4 to his concentration check.
Second Level. temporal concentration that gives him advantage on all of his attacks. He has a +8 to the concentration check. He can not recover the advantage to attacks if broken, however, he can concentrate two of his spell attacks at once.
Third Level. Split Timelines concentration that allows a previous version of himself to concentrate a spell for a prolonged time. If this spell is broken, he looses all of the Temporal Concentration buffs. He has a +12 to the concentration check, and it can only be affected by magical attacks.

Temporal Multiattack. The chronomancer can choose to skip a round of attacks to roll 1d4 on his next turn to perform that many attacks. He will get at least 1 extra attack during this turn. He can only use Time Break Once per turn.

Unmake. (Recharge 1-2) 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 10 (2d10) necrotic damage on a failed save, or half as much damage on a successful one.

Chronobolt. (Recharge 3-4) Ranged spell attack: +10 to hit. reach 150 ft., 1 target. Save DC of 18. Hit: 12 (2d12). On a successful hit, the target looses their bonus turn for the next round.

Temporal swarm. (Recharge 5) Ranged spell attack: +8 to hit. reach 150 ft., 10 targets. Save DC of 16. Hit: 2 (1d4).

Time Break. (Recharge 6) Melee spell attack: +10 to hit. reach 5 ft., 1 target. Save DC of 18. Hit: 10 (2d10) on a successful hit the chronomancer can choose one of the following effects.
Forced Time Jump. Target hit must make a Wisdom DC 16 saving throw or be teleported in line sight of the chronomancer.
Aged. Target makes Constitution DC 16 saving throw or take 10 (2d10) necrotic damage ignoring resistances.

Reality Flux. (1/Day) As a reaction, the chronomancer can force you to fail a saving throw.

Slow Projectile. (Recharge 3-6) If the chronomancer is targeted by a ranged attack, it can alter the flow of time nearby, causing incoming projectiles to slow down. For this attacker's turn, the chronomancer has a +10 bonus to AC.

Stop. (Requires Mythical Change. 1/Week) On an attack that would have killed him completely, the chronomancer can have his alternate self cast time stop. This action can not be performed if his 3rd layer of concentration is broken.

The 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. The chronomancer regains spent legendary actions at the start of its turn.

Time Steal. (Costs 3 actions) The chronomancer chooses one target to make a Con DC 16 saving throw. On a failure, the chronomancer steals the targets reaction, bonus action, or action. On a success, he steals only the targets reaction.

Temporal Sprites. (Costs 1 per Sprite) The chronomancer causes shattering in time around him causing temporal sprites to form. They take an immediate turn upon their summon, but then take their turn on his turns.

Upon reaching 0 HP, the chronomancer rewinds the last turn completely. Any and all effects are reversed, and he returns to the moment before the battle. He then gains the featured mythical effects.
Lore. Understanding now that this is no mere battle of weaklings, but instead a battle for his life, he becomes serious. He pulls upon the temporal powers and multiple versions of himself assist him with this battle. His eyes glow a bright blueish hue and runes appear in the air around him.

Out of Phase. The chronomancer has no order in the initiative. Instead, it can choose to take its turn for this round at the end of any other creature’s turn.

Time Bubble. (Recharge 1) The chronomancer explodes with temporal energies in a 25 ft. range around him. He forcefully rips the bubble out of time, causing him to vanish from other's sight, and them to vanish from his. He no longer exists in that time, and the only thing remaining is a rune on the floor. For every turn that he remains in the bubble, he casts Return on himself. The rune has an HP pool of 50, and has an AC of 8. If destroyed, the bubble will break and he looses a concentration layers 1-2.

Return. (Recharge 2-3) The chronomancer rewinds time to when he was full of power. He regains 6d4 HP. He also rolls an extra recharge.