Warlock Assassin

Assassinate. During its first turn, the assassin 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 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 assassin that isn't incapacitated and the assassin doesn't have disadvantage on the attack roll.

Innate Spellcasting. The warlock’s innate spellcasting ability is Charisma.

Spellcasting. The warlock is a 4th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 15, +7 to hit with spell attacks). It regains its expended spell slots when it finishes a short or long rest. It knows the following warlock spells:

Cantrips (at will): chill touch, eldritch blast, guidance, mage hand, minor illusion, prestidigitation, shocking grasp

1st–5th level (3 5th-level slots): armor of Agathys, arms of Hadar, crown of madness, clairvoyance, invisibility, detect thoughts, fly, dissonant whispers, summon lesser demons, [spell]shadow blade/spell]

Devil’s Sight

 You can see normally in darkness, both magical and nonmagical, to a distance of 120 feet.

Mask of Many Faces 

You can cast disguise self at will, without expending a spell slot.

Multiattack. The assassin makes two shortsword attacks.

Nine Lives Stealer. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 8 (1d6 + 5) 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.

Light Crossbow. Ranged Weapon Attack: +6 to hit, range 80/320 ft., one target. Hit: 7 (1d8 + 3) 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.