Assassinate. During its first turn, the Undertaker Talon 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 Undertaker Talon 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 Undertaker Talon deals an extra 14 (3d6) 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 Undertaker Talon doesn't have disadvantage on the attack roll.
Poisoned Weapons. When the Undertaker Talon hits an enemy with a weapon attack, the target must make a DC15 Constitution saving throw, taking 24 (7d6) poison damage and becoming poisoned for 1 minute (save ends) on a failed save, or half as much damage on a successful one. Poisoned Weapons doesn't affect a target that is already poisoned. The target has disadvantage on the save when hit with a critical.

Multiattack. The Undertaker Talon makes two shortsword attacks.
Shortsword. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) piercing damage. If the target is not poisoned, it must make a DC 15 Constitution saving throw, taking 24 (7d6) poison damage and becoming [condition]poisoned[/poisoned] for 1 minute (save ends) on a failed save, or half as much damage on a successful one.
Throwing Daggers. Ranged Weapon Attack: +6 to hit, range 80/320 ft., one target. Hit: 5 (1d4 + 3) piercing damage. If the target is not poisoned, it must make a DC 15 Constitution saving throw, taking 24 (7d6) poison damage and becoming [condition]poisoned[/poisoned] for 1 minute (save ends) on a failed save, or half as much damage on a successful one.
Modify Memory (3/day). The Undertaker Talon releases a magically charged flash of energy in a 10-foot cone. Each creature must make a DC17 Constitution saving throw, or be subject to the Modify Memory