Baharet, The Shadow Hand

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

Sneak Attack. Once per turn, the assassin deals an extra 42 (12d6) 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 assassin that isn't incapacitated and the assassin doesn't have disadvantage on the attack roll.

Magic Weapons. Baharet's sword is considered magical.

Innate Spellcasting. His spellcasting ability is Intelligence (spell save DC 18, +8 to hit with spell attacks). Baharet can innately cast these spells with no material opponents required.
At will: invisibility, misty step
3/day each: silence, greater invisibility
1/day: project image

Multiattack. Baharet can make two attacks with his shortsword.

Shortsword. Melee Weapon Attack: +10 to hit, reach 5ft., one target. Hit: 12 (1d6 + 8) piercing damage. 

Hidden Sentinel. When invisible, if an ally of Baharet is attacked within 5ft. of him, he can use his reaction to make a melee attack on the attacking creature. This type of reaction does not break his invisibility.