Elemental Exchange (Cold)

You can quickly manipulate the elemental energy of your offensive magic so that it produces ice. When you successfully deal damage with a spell, you can change one of the damage types to cold, so long as you can see the damaged creature. 

When you alter a spell this way at higher levels, add cold damage: +1 at 5th level, +2 at 11th level, +3 at 17th level.