Arcturos

Adamantine Plate. Arcturos is immune to the additional damage from critical hits.

Magic Resistance. Arcturos has advantage on saving throws against spells and other magical effects

Obliterate Undead. Any undead that moves (this includes being forced), or ends its turn within 30ft. of Arcturos must make a DC 21 Wisdom check. If the enemy fails the check by 2 or more it is destroyed, otherwise it is turned. If the enemy succeeds on its saving throw nothing happens. Any undead must repeat this saving throw each time it ends its turn within 30ft. of Arcturos.

Turn Fiends. Any fiend that moves (this includes being forced), or ends its turn within 30ft of Arcturos must make a DC 21 Wisdom check. If the enemy fails, it is turned. If the enemy succeeds, nothing happens. Any fiend must repeat this saving throw each time it ends its turn within 30ft. of Arcturos.

Protective Aura. Arcturos adds his Charisma modifier to all of his saving throws.

Blue and Silver Ancestry. Any spell that Arcturos casts that deals cold or lightning damage, add an additional damage die to the spell. (Whichever the spell uses.)

Spellcasting. Arcturos is a 17-level spellcaster. His spellcasting ability is Charisma (spell save DC 24, +15 to hit with spell attacks). Arcturos has the following Paladin and Sorcerer spells prepared:
Cantrips (at will): Chill Touch, Fire Bolt, Shocking Grasp, Green-Flame Blade, Booming Blade
1st level (4 slots):Absorb Elements, Command, Sanctuary
2nd level (3 slots): Lesser Restoration
3rd level (3 slots): Counter Spell, Dispel Magic, Hypnotic Pattern, Lightning Bolt
4th level (3 slots): Wall of Fire
5th level (2 slots): Hold Moster
6th level (1 slot): Chain Lightning
7th level (1 slot): Fire Storm
8th level (1 slot): None
9th level (1 slot): None

Multiattack. Arcturos may make either 2 melee weapon attacks, cast 2 spells, or make 1 melee weapon attack and cast 1 spell per turn. Arcturos can not Smite and Multiattack on the same turn.

Smite. Arcturos makes a melee weapon attack, on a hit add an additional 35 (7d8) radiant damage.

Advanced Dragon Breath (Recharge 5-6). Arcturos exhales destructive energy. Each creature in a 30ft. cone in front of Arcturos must make a Constitution saving throw. On a failed save, creature(s) take 50 lightning/cold damage (resistances to one element is not applied, if an enemy resists both elements, they take half.). On a successful save, creature(s) take half that amount. This action can be used while Arcturos is flying.

Action Melee Attack. Melee Weapon Attack: +16 to hit, reach 5 ft., 1 target. Hit: 34 (5d8 + 12) magical slashing damage. Fiends and Undead take an additional 2d10 radiant damage. This attack is always non-lethal.

Shield. If an enemy attacks Arcturos and beats his AC by less than 5 and does not land a critical hit, roll a d20. On an 11 or higher, Arcturos casts the shield spell. This reaction can only be used 5 times and does not expend a spell slot when used.

Spellcast. Arcturos can cast any of the spells on his spell list as a reaction.

Arcturos 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, unless specified otherwise. Arcturos regains spent legendary actions at the start of his turn.

Quickened Spell (Costs 1 Actions). When Arcturos casts a spell that has a casting time of 1 action, change the casting time to 1 bonus action for this casting. This Legendary Action can be used on Arcturos' turn.

Light of Bahamut (Costs 2 Actions). This can only be taken when on the end of the turn a creature dealt damage to Arcturos, and Arcturos did not already take a reaction. Arcturos points his sword at the creature (who ended its turn), a beam of light erupts from the tip of the sword dealing 35 (7d8) radiant damage to the creature. A creature cannot be reduced to 0 hit points with this attack; instead if a creature would be reduced to 0 hit points, they are reduced to 1 hit point and fall unconscious for 4d6 hours and cannot be awoken by any other means.