Special Trait Name. Undead Terror

At beginning of combat everyone who enters within 120 ft. makes a dc 22 wis saving throw. On a failed throw target becomes frightened and takes 3d12 necrotic damage. On a success target takes no damage and is not frightened.

Special Trait Name. Shadow Pool

When Undead Knight Commander is at half hp everyone within 60 ft. makes a dc 20 con saving throw. On a failed throw target(s) take 10d10 necrotic damage and is poisoned. On a success target(s) take half damage.

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

Action Name.  Attacks x5

Melee Attack. Shadow Sword: +18 to hit, reach 10 ft., 1 target. Hit:  (3d12 + 10) [slashing and necrotic] damage

Nightmare Attacks x2

Stomp +10 to hit, 5 ft., anyone within 5 ft. Hit: (2d10 + 10) [bludgeoning] damage

Ranged Attack. Shadow Spear

If no one is within melee range of the Undead Knight makes a ranged attack.

Shadow Spear: +15 to hit, reach 120 ft., 1 target. Hit: (3d12) [necrotic and piercing] damage 

Reaction Name. Reflective Armor

As a reaction Undead Knight uses their reaction to reflect any damaging spells that don't do radiant damage.

The Undead Knight Commander 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. Undead knight Commander regains spent legendary actions at the start of its turn.

Attack. Can make one attack with its sword or can throw a spear.

Move. Can move half its walking speed

Terror. Can use its Undead terror [costs two actions]

Enter the description for how mythic actions work for your monster here.

Mythic Action Name (Costs # Actions). Enter the description for your mythic action.