Winter Wraiths are rogues who learn to manipulate ice and cold to cripple their enemies before moving in for the kill. They can use the cold to create thick clumps of mist and freeze enemies. Merciless and cold, they weaken and confuse enemies and strike when the time is right. Their knowledge of icy magic allows them to debilitate their foes, while keeping themselves safe from harm by being out of sight and disorienting them.

Bone Chill

Starting at 3rd level, your Sneak Attacks inflict chilling cold to the target, weakening their strength and making them vulnerable to the cold. Whenever you use Sneak Attack against a creature, it is forced to make a Constitution Save (DC: 8 + Proficiency Bonus + Intelligence Modifier). On a failed save, the creature has disadvantage on attack rolls and vulnerability to Cold Damage until the end of its next turn.

Icy Soul

At 3rd level, you gain Resistance to Cold Damage, and gain Expertise in Intimidation if you haven't already.

Permafrost

Starting at 9th level, your touch becomes so cold that when you strike the right spot, your foes are stung with the freezing coldness of your weapon. Whenever you roll a critical hit, you deal an extra 1d8 Cold Damage. 

The extra damage dealt increases to 2d8 at 11th level, and 3d8 at 15th level.

Haunting Mist

Starting at 13th level, you learn to manipulate mist to your advantage, summoning heavily obscuring mist to remain in stealth. While using Hide, you can choose to create a thick cloud of mist centred around you in a 10-foot-radius sphere and heavily obscures the area. While in this mist, you have advantage in Dexterity(Stealth) Checks and can see through the mist. The mist lasts until the end of your next turn, after which it disperses. This feature can be used a number of times equal to your Intelligence Modifier per Short Rest.

Merciless Winter

Beginning at 17th level, your mercilessness becomes evident in your fighting techniques as you chip away the health of your enemies. You get a critical hit on a roll of 19-20, and your critical hits reduce the maximum health of the target by a number of hitpoints equal to your Rogue level.