Intangibility. Impervious to all physical damage.

Spellcasting.  Θάνατος is a 20-level spellcaster. Its spellcasting ability is [+ 12] (spell save DC 14, +15 to hit with spell attacks).  Θάνατος has following all class spells prepared:
Cantrips (at will): [All] 
1st level (infinite slots): [All]

2nd level (infinite slots): [All]

3rd level (infinite slots): [All]

4th level (infinite slots): [All]

5th level (infinite slots): [All]

6th level (infinite slots): [All]

7th level (infinite slots): [All]

8th level (infinite slots): [All]

9th level (infinite slots): [All]

2 actions per turn

Ideation of Righteousness. Upon gazing at any being, death can see when, how and where that thing will die. Death can change these fates at will, but will generally not if not provoked.

Death's Touch. Whenever death touches something the thing must make a dc 13 constitution save or take 2d12 necrotic damage

Chains of Decay. Ranged Weapon Attack: +5 to hit, range 30/5 ft., 1 target. Hit: 15 (3d6 + 6) [slashing] damage. Death throws out his scythe towards one target, it cuts and laches onto the target, who must make a dc 13 strength save, or be pulled towards Death as it recalls the scythe to it's hand.

Scythe of Damascus. Melee Weapon Attack: +4 to hit, range 5 ft., 1 target. Hit: 23 (3d12 + 6) [slashing and necrotic] damage. Death swings deathly quick with his scythe, cutting all in his way.

 1 Bonus actions per turn

Flight of the Valkyries. Death sprouts wings from his back, gaining 120 ft. of flight.

Blight of the Valkyries. Death flaps his wings, throwing the feathers at any opponents, making them take 2d6 piercing damage.

Resurrect. When any being within 60 ft. of death dies, death can resurrect them, being directly under control, but they can come ack and stay back if they make a dc8 wisdom save.

Shadow Manipulation. Once per every 10 minutes, death can use the shadows to trip, shove, or disrupt an enemy attack, giving them disadvantage on their role.

 1 legendary actions per half hour.

Inescapable Fate. When any being misses a melee attack on death, he can summon ghostly chains from the ground, restraining any being, even beings with immunity to being restrained, holding them there, until they either succeed on a dc20 Strength save, or they stay there for 3 minutes, at which they will be forced into death saves, with disadvantage on the first one.

1 mythic action per minute

Reinstating of Death. Upon dying, death can reincarnate himself as any living being in a 1000 ft. vicinity, morphing them into him, with all his abilities, spells, and actions timer reset, taking there place in initiative.