Undying Knight

Magic Resistance. The undying knight has advantage on saving throws against spells and other magical effects.

Magic Weapons. The undying knight's weapon attacks are magical.

Rejuvenation. When the undying knight is destroyed and its oath has not yet been fulfilled, the undying knight gains a new body in 1d10 days, with all its hit points. The new body appears within 1 mile of where the undying knight previously died. A use of Divine Intervention or a Wish spell can be used to prevent the undying knight from reforming.

Turn Immunity. The undying knight is immune to effects that turn undead.

Spellcasting. The undying 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): cure wounds, searing smite, shield of faith

2nd level (3 slots): branding smite, lesser restoration

3rd level (3 slots): dispel magic, revivify

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

5th level (2 slots): holy weapon

Multiattack. The undying 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) radiant damage.

Smiting Sphere (1/Day). The undying knight hurls a magical ball of burning radiant energy 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) radiant damage and 35 (10d6) fire damage on a failed save, or half as much damage on a successful one.

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