Way of the Frostbitten Heart

Far in the northern edges of the world, ancient orders of monks practice focusing their ki and using it to drain heat from the air, creating deadly bursts of frigid wind. These icy monks use their knowledge of martial arts to get close to an opponent before blasting them with killer frost. 

Icy Strikes

Starting at 3rd level, your unarmed strikes carry the frozen power of your ki. When you hit a creature with an unarmed strike, you can spend 1 ki point to deal extra cold damage equal to two rolls of your Martial Arts die. You can use this feature once per turn. You can use it twice per turn at 6th level, three times per turn at 11th, and four at 17th

Frozen Defender

Starting at 6th level, you have learned to focus your ki and create a layer of frost to protect yourself from harm. Immediately after you take the Attack action on your turn, you can spend 2 ki points to cast the armor of agathys spell as a bonus action. You can spend additional ki points to cast armor of agathys as a higher-level spell. Each additional ki point you spend increases the spell's level by 1. The maximum number of ki points (2 plus any additional points) that you can spend on the spell equals half your monk level.

Binding Ice

Starting at 11th level, you can empower your Icy Strikes to freeze your foes in place. When you damage a creature with your Icy Strike, you can spend an additional ki point to force the target to make a Constitution saving throw. On a failed save, the target's speed becomes 0 until the end of your next turn.

Wintry Blast

Starting at 17th level, you can channel your ki into a large blast of frigid air. You can use your action to cast cone of cold. The first time you use this feature after a long rest, it cost no ki points. Afterwards, you can spend 5 ki points to cast it again.