Aspect of Zathroth, the Apathetic

Aspect of Divinity. If the aspect would be reduced to 0 hit points, his current hit point total instead resets to 522 hit points, he recharges Spark of Creation, and he regains any expended uses of Divine Resistance. Additionally, the aspect can now use the options in the "Mythic Actions" section for 1 hour. Award a party an additional 155,000 XP (310,000 XP total) for defeating the aspect of Zathroth after Aspect of Divinity activates.

Aura of Anti-Life. Whenever a creature within 30 ft. of Zathroth regains hit points (via spell, potion, etc.) that creature must make a DC 19 constitution saving throw. On a success, the creature regains hit points as normal. A creature failing the saving throw instead heals the minimum number of hit points possible.

Divine Resistance (5/Day). If Zathroth fails a saving throw, he can choose to succeed instead. When succeeding with this ability, every creature within 30 feet of Zathroth takes 11 (2d10) radiant damage. 

Limited Magic Immunity. Unless he wishes to be affected, Zathroth is immune to spells of 3rd level or lower. He has advantage on saving throws against all other spells and magical effects.

Magic Weapons. Zathroth’s weapon attacks are magical.

One with the Void. Zathroth can maintain concentration on two different spells at the same time. In addition, he has advantage on saving throws to maintain concentration on spells.

Reality Warper. Any time Zathroth is targeted by a spell that can effect him, such as a magic missile spell, a line spell, or a spell that requires a ranged attack roll, roll a d10. On a 1-8, Zathroth is affected normally. On a 9, Zathroth is unaffected. On a 10, Zathroth is unaffected, and the effect is reflected back at the caster as though it originated from Zathroth, using Zathroth’s spell save DC, turning the caster into the target.

Regeneration. If Zathroth has at least 1 hit point, he regains 30 hit points at the start of its turn.

Multiattack. Zathroth can use Apathy or Corruption. He then makes two attacks: one Emptiness attack and one attack with Voidbringer.

Apathy. Zathroth targets one creature it can see within 150 feet of it. The target must succeed on a DC 23 Wisdom saving throw or become affected as if by the slow spell for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Corruption. Zathroth targets one creature it can see within 150 feet of it. The target must succeed on a DC 23 Constitution saving throw or take 21 (6d6) necrotic damage and become corrupted for 1 minute.

A corrupted creature’s flesh twists in alien ways. The creature has disadvantage on attack rolls, its speed is reduced by half, and if it tries to cast a spell, it must first succeed on a DC 19 Intelligence check or the spell fails and is wasted. The corrupted creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Voidbringer. Melee Weapon Attack: +21 to hit, reach 15 ft., one target. Hit: 34 (6d6 + 13) force damage and 14 (4d6) psychic. Whenever an attack reduces a creature to 0 hit points, the sword slays the creature and devours its soul. A creature whose slain in this way can only be restored to life by a wish spell.

Emptiness. Ranged Spell Attack: +15  to hit, range 150 ft., one target. Hit: 11 (2d10) cold damage, 11 (2d10) force damage, and 11 (2d10) psychic damage.

Spark of Creation (1/day). Zathroth the Apathetic, one of the original creator gods, uses his divine powers to create a new universe in the palm of his decaying hand. He then collapses this new reality into a singularity and releases the awesome divine energy around him. Every creature within 150 ft. of Zathroth, must succeed on a DC 23 Constitution saving throw or take 70 (20d6) force damage and 70 (20d6) psychic damage on a failed save, or half as much damage on a successful save. Any creature failing this save by 5 or more is paralyzed for 1 minute.

Spellcasting. Zathroth is a 40th-level spellcaster in his Aspect form. His spellcasting ability is Charisma (spell save DC 23, +15 to hit with spell attacks):

At Will (5th level): bane, blindness/deafness, chaos bolt (psychic damage only), chill touch, crown of madness, dispel magic, erupting earth, fear, magnify gravity, pulse wave, shocking grasp, thunderwave

2/day each: chain lightning, disintegrate, flesh to stone, forcecage, gravity fissure, mental prison

1/day each: psychic scream, ravenous void, reality break, dark star

Breakthrough. At the start of Zathroth's turn, if he is Paralyzed, Restrained, or Stunned, it can choose to take 5 psychic damage (cannot be reduced) and end the condition(s).

Fold Reality. Zathroth teleports, along with any equipment he is wearing or carrying, up to 60 feet to an unoccupied space he can see. He can cause each creature of his choice within 15 feet of his destination space to take 10 (3d6) psychic. If at least one creature takes this damage, Zathroth regains 50 hit points.

Creator Magics: Zathroth can cast the following spells as a Bonus Action:

3/day each: divine word, finger of death, power word pain

2/day each: crown of stars, power word stun, reverse gravity

1/day each: maddening darkness, power word kill, weird

Zathroth can take up to three reactions per round but only one per turn, and cannot take the same reaction twice in a row.

Read the Pattern. When Zathroth is threatened by a weapon attack he can see, he can use his reaction to impose disadvantage to the attack roll.

Sever the Weave. Zathroth utters a dread word to interrupt a creature he can see that is casting a spell. If the spell is 5th level or lower, it fails and has no effect. If the spell is 6th level or higher, Zathroth makes an Intelligence check (DC 10 + the spell’s level). On a success, the spell fails and has no effect. Whatever the spell’s level, the caster takes 10 (3d6) psychic damage if the spell fails.

Void Retribution. In response to being hit by an attack, Zathroth utters a fell word, dealing 10 (3d6) necrotic damage to the attacker, and Zathroth teleports, along with any equipment he is wearing or carrying, up to 30 feet to an unoccupied space he can see.

Zathroth can take 5 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. Zathroth regains spent legendary actions at the start of his turn.

Attack. Zathroth uses Emptiness or Voidbringer.

Wellspring of Power. Zathroth casts an at will spell.

Rearrange (2 actions). Zathroth can teleport himself, and up to 2 other creatures he can see (Charisma save DC 23 to negate) up to 60 feet to an unoccupied space he can see.

Arcanum Infinitum (3 actions). Zathroth casts a spell.

If the aspect’s Aspect of Diviinty trait has activated in the last hour, he can use the options below as legendary actions.

Hurl Through Time (Costs 2 Actions). Zathroth targets one creature it can see within 150 feet of it. The creature must succeed on a DC 23 Charisma saving throw or take 44 (8d10) psychic damage and be banished to the Void (the realm beyond the Divine Gate). At the start of the aspect’s next turn, the creature reappears in an unoccupied space within 10 feet of the aspect.

Lances of Creation (Costs 3 Actions). The aspect conjures four enormous lances of magical force that plummet to the ground at four different points he can see within 150 feet of him and then disappear. Each creature in a 40-foot-radius, 100-foot-high cylinder centered on each point must succeed on a DC 23 Dexterity saving throw or take 28 (8d6) force damage. A creature in the area of more than one lance is affected only once.