Byftagore

Magic Resistance. Byftagore has Advantage on saving throws against spells and other magical effects. 

Ancient Wisdom.(2/Day) Byftagore can reveal his spellbook, which is normally hidden in a separate dimension, until the end of his turn. Whenever he deals damage with an attack or spell during this turn, he adds his proficiency bonus to each damage roll.

Guidance to Destruction. Byftagore grants, at the start of combat, all his allies Guidance once each per combat, when an ally drops to 20% or less of their max hit points, Byftagore can then choose to invert his guidance to cause them to self-destruct, this is triggered at the end of the current turn, killing them and dealing 8d8 fire damage to all creatures in a 15 feet radius centered on the ally that died, unless they spend a reaction and succeed on a DC 20 Dexterity saving throw, success means they take halved damage. The ally dies immidiently, as such this ability can only be used once per ally.  This cannot be used on the same ally as No room for failure. This ability can not be stopped, but if an ally of Byftagore is healed above 20% max hit points before the end of the current turn, then this trait is not viable until said ally drops below 20% max hit points again. 

Legendary Resistance (3/Day). If Byftagore fails on a saving throw, he can choose to succeed instead. 

Multiattack. Byftagore makes four Arcane Burst attacks, and can choose to replace two of those arcane blasts with Spellcasting. to cast either Fireball (level 8 version) or Chain Lightning(level 8 version) or Ice Storm (level 8 version). 

Arcane Burst. Melee or Ranged Attack Roll: +14, reach 5 ft. or range 150 ft. Hit:  (4d10 + 8) Force damage.

Spellcasting. Byftagore casts one of the following spells, using Intelligence as the spellcasting ability (spell save DC 22):

At Will: Detect Magic, Detect Thoughts, Disguise Self, Invisibility, Light, Mage Armor (included in AC), Mage Hand, Prestidigitation
4/Day Each: Fly, Chain Lightning (level 8 version), Fireball (level 8 version), Ice Storm (level 8 version)
2/Day Each: Cone of Cold (level 9 version), Mind Blank (cast before combat), Scrying

Dimension Door(3/Day). Byftagore casts Dimension Door, using the same spellcasting ability as Spellcasting.

Gifted with eternal life (1/Day). Byftagore draws upon his endless vigor to recover 5d12 + 20 hit points. 

Protective Magic (5/Day Each). Byftagore casts Counterspell or Shield in response to the spell’s trigger, using the same spellcasting ability as Spellcasting.

No room for failure (2/Day). Byftagore casts Fireball (level 8 version) at an allies position in response to that ally dropping to 5% of their maximum hit points, using the same spellcasting ability as Spellcasting. Byftagore's ally is automatically hit and killed. 

Byftagore the Great Mage. Byftagore has access to two legendary actions every round, which refreshes at the start of his turns. Should Byftagore want to use Resistance Is Futile. then he must telegraph this by levitating into the air and state that Resistance is Futile.

Resistance Is Futile - 2 Legendary Actions.(1/Day) Byftagore cast Meteor Swarm, using the same spellcasting ability as Spellcasting, this does prevent him from using any other legendary action prior or after in the same round.

Guide to a brighter future - 0 Legendary Actions.(1/Day)  In his final moments after being defeated before his death, Byftagore uses the last of his strength and remainder of his life force to grant the players who killed him a +2 modifier to any one ability score, up to 30, of their choosing each.

Secrets of Eternity - 1 Legendary Action. Byftagore teleports into a separate dimension and reappears in a location within 100 feet from where he stood when he first used this legendary action.

Kingmaker - 2 Legendary Actions.(1/Day)  Byftagore can choose one ally within 200 feet and visible to him, healing that ally to full hit points and giving them advantage on attacks against the player that has dealt the most damage during this combat, they also gain the "Crown of the Eternal Empire", which grants them resistance to all non-force damage magical attacks. Using this ĺegendary actions makes Byftagore temporarily leave combat and is not available as a target until this ally's hit points have dropped to zero, Byftagore also can not participate in the battle in any way during this period. The crown can be removed early if Wish is used to wish it away or used to destroy it, the crown can not be given to another creature under any circumstances. If this ability is used on Kaelen Voss, then he will instead be restored to full hit points before then having his stat block changed to Kaelen Voss, The chosen King.