I have two spell ideas.

The first is blizzard in the water book. This book has rimefang which may make this overkill. Rimefang has utility to be able to use cyclic tm in places fire rain is not possible. Anyway, blizzard would be a cyclic tm spell similar to fire rain but ice damage instead of fire. Ice damage would be less than fire damage from fire rain. In addition it would either slow foes attack speed by a percentage or a chance of attack speed to be longer. In that regard it would teach target magic and debilitation when the weapon speed debuff is activated.

My second idea is scrap ys. There has been sentiment expressed by the devs to improve it but how they were not sure. Instead of ys move it to the aether book. It would be called elemental armor. You could use it with summoning. So you would prepare it then cast to an element

The effects
Air: its current incarnation
Earth: increased armor protection
Ice: slows enemies attack speed when striking mage
Electricity: either chance to stun or chance to cause a tingle effect when striking mage
Fire: chance for splash fire damage like a fireball or damages a weapon when striking mage