Combining the lack of light -shadow- with a material of lesser temperature -ice- makes it take on its properties, enhancing its pre-existing aspects of missing energy by also removing heat.
The lack of light does not imply the lack of heat, but the lack of heat does imply the lack of light. This is basically a direct upgrade to shadow magic, hence why it might as well just be thought of as darkness magic.
Life magic
Light is commonly seen as a source of life (specifically on the surface), while wood is organic matter stemming from life.
Slash&Blunt magic (basically pressure, but it can't be pressure since that's a gravity upgrade somehow)
What does glass magic do? It cuts you up and hits you with glass (a blunt impact if it isn’t sharp). What does slash magic do? It cuts you up.