Bensvelk, The Brilliant

Arcane Spirit. Bensvelk weapon attacks are magical and gain a +3 bonus to attack and damage rolls (included in the attacks). His spell save DC also increases by 4 and his spell attack bonus increases by 5. Bensvelk can also cast up to two leveled spells a turn rather than one.

Esoteric Transformation (Recharges after a short or long rest). If Bensvelk would be reduced to 0 hit points, his current hit point total instead resets to 292 hit points, he recharges his Breath Weapon, and he regains any expended uses of Legendary Resistance. Additionally, Bensvelk can use the options in the “Mythic Actions” section for 1 hour. Award the party an additional 155,000 XP (310,000 XP total) for defeating Bensvelk after his Esoteric Transformation activates

Focused. Bensvelk can concentrate on up to 3 spells at once. If he needs to make a Constitution saving throw to maintain concentration he makes a separate roll for each spell he is currently concentrating on.

Freedom of Movement. Bensvelk ignores difficult terrain, and magical effects can’t reduce his speed or cause him to be restrained. He can expend 5 ft. of movement to escape from non-magical restraints or being grappled.

Prophetic Dreams. At the end of a long rest, Bensvelk rolls seven d20s. Bensvelk can replace any d20 roll of a creature that he can see including his own with one of these rolls. 

Legendary Resistance (5/day). If Bensvelk fails a saving throw, he can choose to succeed instead.

Limited Magic Immunity. Bensvelk can’t be affected or detected by spells of 7th level or lower unless he wishes to be. He has advantage on saving throws against spells and other magical effects.

Many Arms. Bensvelk can take one reaction per turn, rather than only one per round.

Planes Walker. Bensvelk can breathe in any environment and does not suffer negative effects as a result of being in a plane he is not native to.

Regeneration. Bensvelk regains 10 hit points at the start of his turn.

Special Equipment. Bensvelk wields The Sceptre of Mystic Mastery and The Grimoire of Mystic Wonders (accounted for in his statistics). As an action Bensvelk can absorb the staff into his form, maintaining any benefits the staff grants. He can summon the staff next to him as a bonus action. If Bensvelk enters a medium humanoid form he can also gain the benefits of his robe of the archmagi.

Spellcasting. Bensvelk is a 20th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 37, +30 to hit with spell attacks). Bensvelk has the following wizard spells prepared:
Cantrips (at will): druidcraft, mage hand, dancing lights, fire bolt, eldritch blast, guidance, control flames, prestidigitation
1st level (at will): shield, magic missile
1st level (7 slots): cure wounds, witch bolt, detect magic, hex, sleep, protection from evil and good
2nd level (at will): detect thoughts, fortune's favor
2nd level (6 slots): healing spirit, arcane lock, suggestion, moonbeam, blur
3rd level (at will): speak with plants
3rd level (6 slots): blink, counterspell, magic circle, lightning bolt, dispel magic
4th level (5 slots): banishment, arcane eye, Otiluke’s resilient sphere, dimension door, fire shield
5th level (5 slots): temporal shunt, conjure elemental, hold monster, cone of cold, wall of force
6th level (4 slots): primordial ward, globe of invulnerability, disintegrate, sunbeam, investiture of ice
7th level (4 slots): prismatic spray, forcecage, Mordenkainen's sword, crown of stars
8th level (3 slots): reality break, feeblemind, antimagic field
9th level (3 slots): blade of disaster, foresight
10th level (2 slots)
11th level (1 slot)
12th level (1 slot): Bensvelk’s upend time
13th level (1 slot)

Unwavering Mind. Bensvelk’s thoughts and memories cannot be read or altered unless he allows it, his Intelligence, Wisdom, and Charisma scores cannot be changed, and he is immune to any effect caused by manipulating his mind such as a Mind Flayer’s Mind Blast.

Multiattack. Bensvelk can use his Aura of Awe or Constrict. He then makes four claw attacks. He can choose to replace two of his claw attacks with casting a spell with a casting time of 1 action.

Claw. Melee Weapon Attack: +22 to hit, reach 10 ft., one target. Hit: 23 (4d6 + 13) slashing damage.

Constrict Melee Weapon Attack: +22 to hit, reach 15 ft., one target with a size of huge or smaller. Hit: 24 (2d10 + 13) bludgeoning damage, and the target is grappled (escape DC 26). Until this grapple ends, the target is restrained and moves with Bensvelk, and Bensvelk can’t constrict another target.

 Tail. Melee Weapon Attack: +22 to hit, reach 20 ft., one target. Hit: 26 (4d8 + 13) bludgeoning damage. If the target is a creature it must succeed on a DC 27 Strength saving throw or be knocked prone.

Aura of Awe. Each creature of Bensvelk’s choice that is within 240 feet of Bensvelk and is aware of him must succeed on a DC 27 Wisdom saving throw or become charmed or frightened (Bensvelk’s choice) for 10 minutes. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to Bensvelk's Awesome Aura for the next 24 hours. When Bensvelk uses this ability he can choose any number of different creatures within 240 feet of him to instead gain 30 temporary hit points.

Breath Weapons (Recharge 4-6). Bensvelk uses one of the following breath weapons.

Arcane Breath. Bensvelk exhales arcane energy in a 500-foot line that is 5 feet wide which ignores barriers. Each creature in that area must make a DC 27 Dexterity saving throw, taking 55 (10d10) force damage on a failed save, or half as much damage on a successful one. Instead of rolling for the damage of this breath weapon, Bensvelk can choose to treat the dice as if they rolled their maximum.

Fire Breath. Bensvelk exhales fire in a 300-foot cone. Each creature in that area must make a DC 26 Dexterity saving throw, taking 110 (15d10) fire damage on a failed save, or half as much on a successful one. Instead of rolling for the damage of this breath weapon, Bensvelk can choose to treat the dice as if they rolled their maximum.

Frailing Breath. Bensvelk exhales gas in a 300-foot cone. Each creature in that area must succeed on a DC 26 Constitution saving throw or have disadavntage on attack rolls and their attack damage halved for one minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Change Shape. Bensvelk magically transforms into a humanoid or beast while retaining his game statistics (other than his size). This transformation ends if Bensvelk is reduced to 0 hit points or if he uses an action to end it. Any equipment he is wearing or carrying is absorbed or worn by the new form (Bensvelk’s choice).

Bensvelk 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. Bensvelk regains spent legendary actions at the start of his turn.

Detect. Bensvelk makes a Wisdom (Perception) check.

Spell (Costs 2 Actions). Bensvelk casts a spell of 1st-6th level with a casting time of 1 action

Cantrip. Bensvelk casts a cantrip with a casting time of 1 action

Tail Attack. Bensvelk makes a tail attack

Flying Dash. Bensvelk flies up to his flying speed

Mystic Body. Bensvelk temporarily destroys his body, replacing it with an incorporeal form made of mystic energy. While in this form, Bensvelk can move through other creatures and objects as if they were difficult terrain and has immunity to force, poison; and bludgeoning, piercing, and slashing damage. This effect lasts until the end of Bensvelk’s next turn.

Arcane Rift (2 actions). Roll a d6, Bensvelk picks a spell of a level equal to the number rolled on the die. That spell takes effect at any space or creature within 30 feet of him. Bensvelk does not require any verbal, somatic, or material components and the spell duration instead becomes instantaneous.

Celestial Patterns (3 actions). Bensvelk gazes upwards and draws portents from the patterns of the sky. Bensvelk automatically rolls a 19 on the next d20 roll he makes.