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

Sneak Attack. Once per turn, the cultist 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 cultist that isn't incapacitated and the cultist doesn't have disadvantage on the attack roll.

Undying Spirit. Upon death, the cultist will rise again within the next 1d4 minutes, gaining 4d10 hp. The only way to keep it dead is to destroy the head.

Multiattack. The assassin makes two shortsword attacks.

Shortsword. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) piercing damage, and the target must make a DC 15 Constitution saving throw, taking 24 (7d6) poison damage on a failed save, or half as much damage on a successful one.

Invasion of the Mind. The cultist attempts to invade the mind of an creature within 60ft, having them make a DC16 Wisdom saving throw. If failed, the creature takes 32 (4d12) psychic damage, or half as much on a success, along with disadvantage on attack rolls and saving throws until the cultist's next turn.