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

Born of Shadows. When in dim light or darkness, the shadow fey poisoner is invisible.

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

Fey Ancestry. The shadow fey has advantage on saving throws against being charmed, and magic can't put it to sleep.

Shadow Traveler (4/Day). As a bonus action while in shadows, dim light, or darkness, the shadow fey disappears into the darkness and reappears in an unoccupied space it can see within 30 feet. A tendril of inky smoke appears at the origin and destination when it uses this trait.

Sneak Attack (1/Turn). The shadow fey poisoner deals an extra 21 (6d6) 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 poisoner, that ally isn't incapacitated, and the poisoner doesn't have disadvantage on the attack roll.

Sunlight Sensitivity. While in sunlight, the shadow fey has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Traveler in Darkness. The shadow fey has advantage on Intelligence (Arcana) checks made to know about shadow roads and shadow magic spells or items.