Sneak Attack (1/Turn). The stalker deals an extra 3 (1d6) 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 stalker that isn't incapacitated and the stalker doesn't have disadvantage on the attack roll.  

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  While following the command of a captain, the stalker gains additional abilities based on the captain's level:   2nd. Cunning Action. On each of its turns, the stalker can use a bonus action to take the Dash, Disengage, or Hide action.   6th. Sneak Attack. The stalker's Sneak Attack damage increases to 7 (2d6).   10th. Uncanny Dodge. The stalker can use its reaction to halve the damage it takes from an attack that hits it. The stalker must be able to see the attacker.   10th. Sneak Attack. The stalker's Sneak Attack damage increases to 10 (3d6).   14th. Evasion. If the stalker is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, the stalker instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.   14th. Sneak Attack. The stalker's Sneak Attack damage increases to 14 (4d6).   18th. Assassinate. During its first turn, the stalker has advantage on attack rolls against any creature that hasn't taken a turn. Any hit the stalker scores against a surprised creature is a critical hit.