Chosen of Vecna (Assassin)

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

Chosen of Vecna. The assassin has advantage on saving throws against being stunned, on Charisma (Deception) made to lie, and Wisdom (Insight) checks to determine whether someone is lying to it. Additionally, the assassin is immune to the detect thoughts spell and other magical effects that would read its mind.

Deathless Emissary. The assassin has advantage on Constitution and Death saving throws, and it can speak all languages (included above).

Semi-Corporeal. The assassin can move through a space as narrow as 1 foot wide without squeezing and has advantage on saving throws to avoid or end any of the following conditions: grappled, paralyzed, petrified, or restrained.

Shadow Stalker. Magical darkness doesn't impede the assassin's darkvision. Additionally, when the assassin takes the Dodge action, opportunity attacks against it have disadvanatge.

Sneak Attack (1/Turn). The assassin 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 assassin that isn't incapacitated and the assassin doesn't have disadvantage on the attack roll. Additionally, the assassin can target a second creature that it can see within 30 feet of the first creature. The second target takes 10 (3d6) necrotic damage.

Sunlight Sensitivity. While in sunlight, the assassin has disadvantage on attack rolls, ability checks, and saving throws.

Unarmored Defense. The assassin's AC includes its Wisdom modifier.

Multiattack. The assassin makes one Ghostfire Blade attack, one Psychic Dagger attack, and one Spectral Fist attack.

Ghostfire Blade. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 9 (1d6 + 6) slashing damage plus 3 (1d6) fire damage and 7 (2d6) necrotic damage. If the target is a creature, it must make a DC 17 Constitution saving throw or have its Constitution score reduced by 1d4. The target dies if its Constitution is reduced to 0. The reduction lasts until the target finishes a short or long rest.

Psychic Dagger. Melee or Ranged Weapon Attack: +10 to hit, reach 5 ft. or range 30/120 ft., one target. Hit: 8 (1d4 + 6) piercing damage plus 7 (3d4) psychic damage and the target must make a DC 17 Intelligence saving throw or be stunned until the end of its next turn.

Spectral Fist. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 10 (2d4 + 5) force damage and the target must make a DC 17 Strength saving throw or be knocked prone.

Assassin's Instinct. The assassin takes the Dash, Disengage, Dodge, or Hide action.

Shadow Jump. The assassin can teleport up to 30 feet to an unoccupied space it can see. Both the place it teleports from and its destination space must be in dim light or darkness.

Spectral Flurry (5/Day). The assassin makes two Spectral Fist attacks.

Sublimating Defense. When the assassin takes damage, it can become incorporeal and give itself resistance to the triggering damage. Additionally, until the end of the assassin's next turn or until it damages a creature, it has resistance to all damage and can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.