Winter Witches are those who draw upon the depths of winter for their magic. A time of darkness, cold, even death, their magic reflects this, and it gives them something of a sinister reputation. This is not entirely deserved though. While some are wicked tyrants who terrorize those who enter their domains, many winter witches instead take up this path in order to provide others with shelter and guidance in the depths of winter, to aid in their survival.
When you select this archetype at 2nd level you learn the ray of frost cantrip if you do not know it already.
In addition, all cold spells count as witch spells for you and whenever you cast a cold spell of 1st level or higher, it counts as being one spell slot higher than you actually expended, to a maximum of the highest level spell slot you possess. In the case of fire shield and infernal weapon, this benefit only applies when casting the cold version.
At 6th level, you ignore the effects of extreme cold and can survive even in incredibly cold temperatures without need for shelter or protective clothing and ignore difficult terrain caused by snow or ice. You also gain 60 feet of darkvision if you do not already have it.
At 10th level, whenever you cast a spell that deals fire or lighting damage, you may cause it to deal cold damage instead. If you do so, it counts as a cold spell for the purposes of heart of winter.
At 14th level you always have the flesh to stone spell prepared and it doesn't count against your number of prepared spells. It counts as a cold spell for you and you can cast it without expending a spell slot at 6th level once per long rest. It turns the creature into ice rather than stone, though this ice does not melt normally.