Black Finger 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.

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

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.  This attack is also in effect if the assassin is hidden and the target does not see the attack coming.

Multiattack. The assassin makes three dagger attacks, or one crossbow attack.

Dagger. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 7 (1d4 + 8) piercing damage, and the target must make a DC 15 Constitution saving throw, taking 12 (3d6+2) poison damage on a failed save, or half as much damage on a successful one.

Light Crossbow. Ranged Weapon Attack: +8 to hit, range 80/320 ft., one target. Hit: 9 (1d8 + 6) piercing damage, and the target must make a DC 15 Constitution saving throw, taking 15 (4d6+2) poison damage on a failed save, or half as much damage on a successful one.

Cunning Action.  The assassin can take a bonus action on each of their turns in combat. This action can be used only to take the Dash, Disengage, or Hide action.

Uncanny Dodge.  When the assassin is attacked by someone they can see, they can use their reaction to halve the attacker's damage against them.