Blackstar Knight

Immutable Form. The blackstar knight is immune to any spell or effect that would alter its form.

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

Magic Weapon. The blackstar knight's weapon attacks are magical.

Multiattack. The blackstar knight makes four melee attacks in any combination.

Deathsword. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 14 (2d6 + 7) slashing damage plus 9 (2d8) necrotic damage. If the target is a creature, it must succeed on a DC 19 Wisdom saving throw or be deathmarked. While deathmarked, a creature takes 9 (2d8) necrotic damage at start of each its turns. A creature can use an action to repeat the saving throw on each of its turns, ending the effect on itself on a success.

Slam. Melee Weapon Attack: +11 to hit, range 5 ft., one target. Hit: 16 (2d8 + 7) bludgeoning damage. If the target is a creature, it must succeed on a DC 19 Strenght saving throw or be knocked prone.

Blackstar Lightning. Ranged Spell Attack: +8 to hit, range 120 ft., one creature. Hit: 45 (10d8) necrotic damage and each other creature within 10 feet of the target takes 9 (2d8) necrotic damage. Each creature that takes damage must succeed on a DC 19 Constitution saving throw or be stunned until the end of its next turn.

Undying Duty (1/Day). When the blackstar knight is reduced to 0 hit points, it can target any number of creatures within 10 feet of it, dealing 11 (2d10) necrotic damage to each undead and 5 (1d10) necrotic damage to all other creatures, regaining lost hit points equal to the total damage dealt.