Cryomancy is cool, ice is cool and ice mages too. But does it actually hold any utility other than keeping your food fresh, specially martially wise(?) 

How could an individual with ice magic powers be able to use his magic in combat, a life or death situation where fleeing is not an option ?

The magic works like that : You can activate a part of your brain that enables you to turn air into liquid then solid ice by manipulating pressure or at least to drop it's temperature at the cost of calories, only the air you are able to directly ''see'' so freezing people to death from within is not an option. 

Dropping 100 liters of air down by 10 C° costs 500 Kilocalories and causes extreme acceleration in breathing if this magic is abused it can fatigue or even kill the user.