Death Knight

When a paladin that falls from grace dies without seeking atonement, dark powers can transform the once-mortal knight into a hateful undead creature. A death knight is a skeletal warrior clad in fearsome plate armor. Beneath its helmet, one can see the knight's skull with malevolent pinpoints of light burning in its eye sockets.

Eldritch Power

The death knight retains the ability to cast divine spells. However, no death knight can use its magic to heal. A death knight also attracts and commands lesser undead, although death knights that serve powerful fiends might have fiendish followers instead. Death knights often use warhorse skeletons and nightmares as mounts.

Immortal Until Redeemed

A death knight can arise anew even after it has been destroyed. Only when it atones for a life of wickedness or finds redemption can it finally escape its undead purgatory and truly perish.

Death Knight CR: 17 (18,000 xp)

Medium undead, chaotic evil

Armor Class: 20

Hit Points: 180 (19d8 + 95)

Speed: 30 ft

STR

20 +5

DEX

11 +0

CON

20 +5

INT

12 +1

WIS

16 +3

CHA

18 +4

Saving Throws: Dex +6, Wis +9, Cha +10

Damage Immunities: necrotic, poison

Condition Immunities: exhaustion, frightened, poisoned

Senses: darkvision 120 ft., passive Perception 13

Languages: Abyssal, Common

Challenge Rating: 17 (18,000 xp)

The death knight is a 19th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 18, +10 to hit with spell attacks). It has the following paladin spells prepared:
1st level (4 slots): command, compelled duel, searing smite
2nd level (3 slots): hold person, magic weapon
3rd level (3 slots): dispel magic, elemental weapon
4th level (3 slots): banishment, staggering smite
5th level (2 slots): destructive wave (necrotic)

Magic Resistance. The death knight has advantage on saving throws against spells and other magical effects.
Marshal Undead. Unless the death knight is incapacitated, it and undead creatures of its choice within 60 feet of it have advantage on saving throws against features that turn undead.

Actions

Multiattack. The death knight makes three longsword attacks.
Longsword. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 5) slashing damage, or 10 (1d10 + 5) slashing damage if used with two hands, plus 18 (4d8) 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 18 Dexterity saving throw. The sphere spreads around corners. A creature takes 35 (10d6) fire damage and 35 (10d6) necrotic damage on a failed save, or half as much damage on a successful one.

Reactions

Parry. The death knight adds 6 to its AC against one melee attack that would hit it. To do so, the death knight must see the attacker and be wielding a melee weapon.