Celeste Shame, Fallen Paladin

Unholy Resilience. Unless Celeste is incapacitated, she has a +4 to on saving throws against spells and other magical effects. She is immune to the charmed and frightened conditions. 

Unholy Smite. When Celeste hits with a melee weapon attack, she can expend a spell slot to deal additional necrotic damage to the target, in addition to the weapon's damage. The extra damage is 9 (2d8) necrotic damage for a first level spell slot, plus 4 (1d8) for each spell level higher than 1st, to a maximum of 21 (5d8).

Spellcasting. Celeste is a 12th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 15). She has the following paladin spells prepared:

1st level (4 slots): command, compelled duel, searing smite

2nd level (3 slots): hold person, silence

3rd level (3 slots): dispel magic, bestow curse

Multiattack. Celeste makes two longsword attacks.

Flame Tongue Longsword. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 4) slashing damage, or 9 (1d10 + 4) slashing damage if used with two hands, plus 8 (2d8) necrotic damage.

Hellfire Orb (1/Day). The death knight hurls a magical ball of fire that explodes at a point it can see within 120 feet of it. Each creature in a 20-foot-radius sphere centered on that point must make a DC 15 Dexterity saving throw. The sphere spreads around corners. A creature takes 15 (5d6) fire damage and 15 (5d6) necrotic damage on a failed save, or half as much damage on a successful one.

Parry. Celeste adds 2 to its AC against one melee attack that would hit it. To do so, Celeste must see the attacker and be wielding a melee weapon.

Hellish Rebuke (1/Day). When Celeste is damaged by a creature within 60 feet of her that she can see, the creature that damaged her is engulfed in hellish flames and must make a DC 15 Dexterity saving throw, taking 16 (3d10) fire damage on a failed save, or half as much damage on a successful one.