BBEG Death Knight

Legendary Resistance (3/Day). If the death knight fails a saving throw, it can choose to succeed instead.

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.

Aura of Undead Rage. All non-hostile undead creatures within 15 ft. of the death knight have advantage on all attack rolls.

Wish Resistance. The Death Knight is immune to all effects caused by Wish.

Spellcasting. The death knight is a 19th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 24, +16 to hit with spell attacks). It has the following spells prepared:

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

2nd level (3 slots): hold person, magic weapon, darkness

3rd level (3 slots): dispel magic, elemental weapon, counterspell

4th level (3 slots): banishment, staggering smite

5th level (2 slots): destructive wave (necrotic)

Multiattack. The death knight makes three attacks with its bastard sword and one attack with its hellfire orb or a sweeping attack.

Bastard Sword. Melee Weapon Attack: +18 to hit, reach 5 ft., one target. Hit: 19 (2d8 + 5) slashing damage, plus 18 (4d8) necrotic damage.

Sweeping Attack. Melee Weapon Attack: +18 to hit, reach 15ft., 15ft. cone of targets Hit: 19 (2d8 + 5) slashing damage, 18 (4d8) necrotic damage.4

Hellfire Orb. 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.

Call of the Dead. The Death Knight unleashes an unearthly roar and all creatures not on the ground are forced to descend at a rate of 60 ft. per round.

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.

Riposte. When a creature misses the death knight with a melee attack, the death knight can make a melee weapon attack against the creature.

Revenge. When a creature damages the death knight, it can send the creature, momentarily into the plane of undeath. The creature must make a DC 16 Wisdom saving throw to remain in the material plane. On a failed save, the ordeal deals 65 (12d10) psychic damage to the creature. On a successful save, the creature takes no damage and is immune to the effects of Revenge on all future uses, but is frightened until the start of its next turn.

The death knight 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. The death knight regains spent legendary actions at the start of its turn.

Attack. The death knight makes one bastard sword attack.

Move. The death knight moves up to half its speed.

Spell. The death knight casts a spell.

Unholy Regeneration (Costs 2 charges). The death knight heals for 35 (10d6) hitpoints.

Planar Destruction (Costs 3 charges). The death knight reaches into the plane of undeath and pulls from it pure unholy energy. The death knight points at any location he can see and unholy energy explodes from that point. All creatures within 15 ft. of that point must make a DC 19 Dexterity saving throw. On a failed save, a creature takes 130 (20d12) necrotic damage and 65 (10d12) fire damage, or half as much damage on a success. Undead creatures within the area of the explosion are healed for 25 (10d4) hp.

The Death Knight absorbs the corpses of its fallen allies and regains all of its HP. It is no longer able to summon allies and minions but gains new actions and abilities as detailed below.

Multiattack (Replace the previous Multiattack). The death knight uses corpse explosion if possible, makes four attacks with its bastard sword, and one attack with its hellfire orb or sweeping attack.

Corpse Explosion. The death knight can cause a number of corpses up to its charisma modifier to explode. All creatures within a 10 ft. sphere of the explosion must make a DC 18 Dexterity saving throw.  A creature takes 35 (10d6) fire damage and 35 (10d6) necrotic damage on a failed save or half as much damage on a success.

A Weapon to Rival the Gods of Old (1/day). As a bonus action, the death knight can imbue his bastard sword with unholy power. It deals 28 (4d8 + 10) slashing damage and 75 (10d10 +20) necrotic damage. This effect lasts for 3 rounds.

Wings of Death. The death knight gains a pair of skeletal wings that give him a fly speed of 80 ft. As a bonus action, the death knight can wrap the wings around himself and increase his Armor Class by 5 until his next turn.