Time Warp. Zarthanon switches initiative placement with another creature.

Legendary Resistance (3/day). If Zarthanon fails a saving throw, it can choose to succeed instead.

Gravitic Presence. Any creature of Zarthanon's choice within 60 feet cannot fly or jump and suffers from the effects of difficult terrain.

Singularity Bound. Zarthanon cannot be forcibly moved or teleported unless it chooses to be. Its gravitational anchor roots him to spacetime.

Celestial Rebuke. When Zarthanon falls to 0 hit points, it falls to 1 instead. Each creature of Zarthanon's choice within 30 feet of him is pushed back 15 feet and stunned until the end of its next turn.

Spellcasting. Zarthanon is a 17th-level spellcaster. Its spellcasting ability is Charisma 29 (spell save DC 23, +15 to hit with spell attacks). Zarthanon has the following spells prepared:

• Cantrips (at will): Dancing Lights, Friends, Guidance, Light, Mending, Resistance, Spare the Dying, Thaumaturgy
• 1st Level (5 slots): Bless, Charm Person, Cure Wounds, Detect Evil and Good, Detect Magic, Divine Favor, Ensnaring Strike, False Life, Guiding Bolt, Heroism, Protection from Evil and Good, Sanctuary, Shield of Faith
• 2nd Level (4 slots): Aid, Blindness/Deafness, Calm Emotions, Detect Thoughts, Enhance Ability, Enlarge/Reduce, Healing Spirit, Hold Person, Lesser Restoration, Moonbeam, Prayer of Healing, Skywrite, Suggestion
• 3rd Level (4 slots): Aura of Vitality, Beacon of Hope, Call Lightning, Counterspell, Dispel Magic, Haste, Lightning Bolt, Mass Healing Word, Protection from Energy, Remove Curse, Revivify, Tidal Wave, Water Walk
• 4th Level (4 slots): Aura of Life, Aura of Purity, Banishment, Conjure Minor Elementals, Death Ward, Dimension Door, Divination, Freedom of Movement, Guardian of Faith
• 5th Level (3 slots): Banishing Smite, Bigby's Hand, Cone of Cold, Conjure Elementals, Contact Other Plane, Dispel Evil and Good, Dominate Monster, Hold Monster, Mass Cure Wounds, Modify Memory, Telekinesis
• 6th Level (2 slots): Chain Lightning, Contingency, Disintegrate, Heal, Mass Suggestion, Planar Ally, Sunbeam
• 7th Level (2 slots): Conjure Celestial, Divine Word, Plane Shift, Prismatic Spray, Regenerate, Teleport
• 8th Level (1 slot): Antimagic Field, Demiplane, Dominate Monster, Holy Aura, Power Word Stun, Sunburst
• 9th Level (1 slot): Imprisonment, Mass Heal, Meteor Swarm, Power Word Heal, Power  Word Kill, Time Stop, True Polymorph, Wish

Multiattack. Zarthanon makes three attacks using Judge's Gavel or Heavenly Warbow.

Judge's Gavel. Melee Weapon Attack: +15 to hit, reach 15 ft., 1 target. Hit: 30 (6d6 + 9) bludgeoning damage + 16 (2d6 + 9) radiant damage.

Heavenly Warbow. Ranged Weapon Attack: +15 to hit, range 600/900 ft., 1 target. Hit: 30 (6d6 + 9) radiant damage.

Gravity Enhanced Slam (Recharge 6). Zarthanon flies and strikes the earth with Judge's Gavel at a point it can see within 100 feet of himself. Each creature within a 5 foot radius of the point must make a DC 23 Dexterity saving throw or take 4 (1d8) bludgeoning damage + 4 (1d8) radiant damage. The attack's damage increases by 4 (1d8) bludgeoning damage + 4 (1d8) radiant damage and its radius increases by another 5 feet for each 10 feet Zarthanon descends during the attack. On a successful save, the creature takes half damage.

Radiant Burst (Recharge 5-6). Zarthanon emits a large amount of radiant energy. Each creature within 50 feet of Zarthanon must make a DC 23 Constitution saving throw or take 65 (10d12) radiant damage and be blinded until the end of Zarthanon's next turn. On a successful save a creature takes half damage and is not blinded.

Heavenly Order. Zarthanon casts the command spell on up to 4 creatures within range.

Gravitational Push (Recharge 5-6). Zarthanon increases its AC by 5 until the beginning of its next turn and pushes any creatures within 15 feet 10 feet away.

Gate. Zarthanon teleports to an unoccupied space within 60 feet along with up to 4 willing creatures it can see.

Zarthanon 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. Zarthanon regains spent legendary actions at the start of its turn.

Gravity Pulse (Costs 1 action). Each creature of Zarhathon’s choice within 15 feet must succeed on a DC 23 Strength saving throw or be pushed 15 feet away and fall prone.

Space Warp (Costs 2 Actions).
Zarhathon chooses a point within 60 feet. Until the end of the next round, that space is considered difficult terrain in a 10 foot radius, and creatures inside must make a DC 23 Constitution saving throw or have disadvantage on attack rolls while in it.

Eventide Execution (Costs 3 Actions).
Zarhathon makes one Judge's Gavel attack against each creature in a 10-foot cone. Each hit target must also make a DC 23 Strength save or be pulled directly to Zarhathon and stunned until the end of their next turn.