Curseborn Guardian

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

Spider Climb. The Guardian can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Magic Weapon. The Guardian's weapon attacks are magical.

Multiattack. The Guardian makes two glaive attacks.

Glaive. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit:  16 (2d10 + 5) piercing damage.

Maneuvers (Recharge 5-6). The Guardian can use Whirlwind or Wave of Decay. 

Whirlwind. The Guardian spins its glaive and attacks nearby enemies. Each creature within 10 ft. of the Guardian must make a DC 17 Dexterity saving throw. On a failed save, the creature takes 42 (12d6) slashing damage, is knocked back 10 feet and prone. On a successful save, the creature takes half as much damage with no additional effects.

Wave of Decay. The Guardian unleashes a necrotic wave in a 20 foot cone. Each creature in that area must make a DC 17 Dexterity saving throw. On a failed save, the creature takes 54 (12d8) necrotic damage. On a successful save, the creature takes half as much damage. The wave has no effect on undead or constructs.

Eldritch Weapon.  The Guardian can magically recall its weapon to its hand.