School of Cryomancy

 the Cryomancer wizard uses the cold to help them both offensively and defensively, using ice magic to its limits and going so far as to turn others into literal ice

 

Icy armor

as a bonus action, You can cause strong but relatively light ice to grow all over your body and bolster your armour class, adding your intelligence modifier to it as well as granting you resistance to fire damage for up to one minute before the ice melts off. The caster can also grant the icy "armor" to anyone it touches as a bonus action. You can use this equal to your proficiency bonus before needing to take a long rest to do it again

Cold reflection

A cold sheen of transparent layers of magical ice envelopes your body. Once you are hit by a ranged attack, before you see the damage die, you can use to reaction to automatically return fire with a cold reflection of what you were hit by, thus sending an icy copy of whatever you were hit by back to your attacker or anywhere else within a range equal to a distance from you to your attacker, except it does cold damage. you can do this equal to your proficiency bonus before needing to take a long rest to do it again.

if you were hit by an arrow, and arrow made of ice fires back, if it was a fireball, then a ball of ice heads their way, if its a net, an icy nets goes back their way, etc. You are only reflecting the initial ranged attack back and thus If you reflect a spell that normally has some sort of concentration affect after, that is to be ignored

Mold Cold

You can the ability to manipulate, destroy, and create ice, as well as freeze water. You can destroy or create up to a 5 foot cube, and can freeze a body or section of water no bigger than a 20 foot cube. when manipulating ice, you can do so as a bonus action, functionally using this ability akin to the "Mold Earth" spell

Permafrost

Permafrost grants you 2 abilities:

1. When you touch a willing or unconscious creature, you can petrify them, turning them into a hard, magical ice that does not melt at no cost. You can return them to normal whenever you so choose.

2. When you land an attack that does cold damage on an enemy, in addition to damaging them as normal, you also temporarily reduce their hit point maximum by a number equal to your damage roll. After the target has suffered this effect, they can remove it by spending an action warm themselves up or by taking either a short or long rest

Hypothermia

the prolonged exposure to your icy presence begins to accumulate, hurting them greatly. For every time after the first time you have damaged a target with cold damage within 30 feet of you, they take additional damage equal to an additional 2 damage die for each subsequent time they have been hit after the first. Your maximum additional dice is 4 until level 15, where the maximum additional dice you can have reaches 8

Ex, if you casted cone of cold at 5th level, it would do 10d10 as opposed to 8d10 (assuming this was the second time they took cold damage and they were within 30 feet of you when they were hit) and 12d10 on the third time.

Absolute Zero

As an action, for just a moment you create a sphere of cold, 40 feet in diameter, centring around you where temperatures reach absolute zero, during that short period of time, anyone caught within the area of affect becomes petrified, becoming solid magical ice for one minute, though you can choose to return any creature caught within the blast back to normal as a bonus action. There is no save against absolute zero but you can only use it once per long rest