The Frozen Blade

The blade bursts from the shadow, silencing it's target forever. They will never find the blade that took the life, all it left was a watery mark after it melted away. The perfect crime leaves behind no evidence, making your crimes, not perfect, but close. 'Cold-blooded' suits you perfectly, bringing forth shards of frozen weapons to put your enemies on ice.

Frozen Weapons

3rd Level: As an action you can summon a light melee weapon into your hand, this weapon is made entirely of ice and can be unsummoned as a free action, after which the weapons rapidly melt away becoming untraceable. You can only summon up to two frozen weapons at any one time. Alternatively you can summon ammunition, arrows bolts or bullets.

When you strike a target with a sneak attack using one of your frozen weapons the target's movement is reduced by the sneak attack damage until the start of your next turn.

Layer of Frost

9th level: As an action you can spread light frost over a 5ft squared surface. You can use this frost to detect areas that were touched by warm creatures in the last 12 hours, including handprints and footprints. After the initial spread the frost melts rapidly.

Once per short rest you can use an Bonus Action to spread a layer frost around you in a 10ft radius. This area becomes difficult terrain for 1 minute.

Blizzard's Cloak

13th Level: You have become resistant to Cold damage and when you are struck by a melee attack by a creature within 5ft of you, the creature takes cold damage equal to your proficiency bonus.

Levistian Cage

17th Level: When you attack a creature and would use sneak attack, you can forgo causing the damage to flash freeze your target. The target gains temporary hit points equal to your rolled sneak attack damage. The target remains paralysed and frozen for 1 minute or until it loses the temporary hit points. At the end of each of the frozen creature's turn it can make a Strength saving throw and reduce its own temporary hit points equal to half its roll.

You can use this ability a number of times equal to your Constitution modifier (minimum 1) per short or long rest.