Assassinate. During its first turn, the Killer has advantage on attack rolls against any creature that hasn't taken a turn. Any hit the Killer scores against a surprised creature is a critical hit.

Evasion. If the Killer is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, the Killer instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.

Sneak Attack. Once per turn, the Killer deals an extra 14 (4d6) damage when it hits a target with a weapon attack and has advantage on the attack roll, or when the target is within 5 feet of an ally of the Killer that isn't incapacitated and the Killer doesn't have disadvantage on the attack roll.

Deadly Critical. Killer scores a critical hit on a roll of 19 or 20 and rolls the damage dice three times, instead of twice.

Lightfooted. The Killer can take the Dash or Disengage action as a bonus action on each of its turns.

Legendary Resistance (3/Day). If The Killer fails a saving throw, he can choose to succeed instead.

Magic Weapons. Killer uses Veiled Night and uses it to cast spells.

1/day: darkness, misty step, branding smite, shield.

Multiattack. The Killer makes two melee attacks.

Veiled Night. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 8) piercing damage, and the target must make a DC 15 Constitution saving throw, taking 24 (7d6) poison damage on a failed save, or half as much damage on a successful one.

Parry. The Killer adds 5 to its AC against one melee attack that would hit it. To do so, The Killer must see the attacker and be wielding a melee weapon.

Riposte. When a creature misses The Killer with a melee attack, he can use his reaction and make a melee weapon attack against it. 

Redirect Attack. When a creature misses The Killer with an attack, he chooses another creature within 5 feet of it, and the chosen creature becomes the target instead.

The Killer 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 Killer regains spent legendary actions at the start of his turn.

Quick Step. The Killer moves up to his speed without provoking opportunity attacks.

Attack(Costs 2 Actions). The Killer makes two attack.