Icy Movement. The yuki onna can move through other creatures and objects as if they were difficult terrain. When moving through the space of another creature, the creature must make a DC 16 Constitution saving throw or take 13 (2d12) cold damage, taking half as much on a successful save.  The yuki onna takes 5 (1d10) force damage if she ends her turn inside an object.

Aura of Cold. The yuki onna is surrounded by an aura of frigid cold with a 20 ft. radius which she can turn on or off at will. When a creature enters the aura for the first time or ends its turn within the aura, the target must make a DC 16 Constitution saving throw or take 15 (1d10+10) cold damage, taking half as much damage on a successful save. Any nonmagical flame the target is carrying is extinguished. 

Spirit Lantern. The yuki onna has a number of spirit lanterns that drift near her. In order for them to be detected in icy or snowy environments, it requires someone actively looking and a DC 18 Wisdom (Perception) check. These lanterns appear as faint speckles of light near the yuki onna. 

A yuki onna has 5 (2d4) spirit lanterns at her disposal which she can use in a variety of ways as described below. She does not recover lanterns until a short or long rest or when taking fire damage (see: reactions). 

Spirit Martyr. As a reaction, the yuki onna may have an attack deal damage to a spirit lantern instead of herself. 

Spirit Spike. As a bonus action, the yuki onna expends a spirit lantern and immediately attacks with an additional frigid bolt or frozen touch attack.

Spirit Fire. The yuki onna casts faerie fire with a DC 16 for the Dexterity saving throw the fire showing an icy blue color. 

Spirit Charm. The yuki onna targets a creature within 30 ft. of her. The target must make a DC 16 Wisdom saving throw or be charmed for 1 hour. While charmed in this way, the target wants to be near the yuki onna's side at all times and will defend her with its life. A target succeeding on the saving throw is immune to this charm for 24 hours. 

Freezing Touch. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 17 (4d6 + 3) cold damage plus the target must make a DC 15 Constitution saving throw or take 4 (2d4) Constitution damage as well, the yuki onna healing for the same amount of Hit Points.. If the target is reduced to 0 Constitution in this way, then the creature dies and the yuki onna regains 10 additional Hit Points. On a successful save, the target takes no Constitution damage and the yuki onna is not healed.

Frigid Bolt. Ranged Weapon Attack: +7 to hit, range 300 ft./300 ft., one target. Hit: 31 (2d20+10) cold damage and the target's movement speed is reduced to 10 ft. until the end of the target's next turn. 

Fire Reaction. When the yuki onna takes fire damage, she immediately recovers 1 spirit lantern as a reaction.