Replace monsters’ “ice bolt” spell with a spell of freezing and/or flaming sphere. The intention of this is to make it more tactical to fight early-game spellcasters who currently cast ice bolt.

If you cast flame sphere or freeze sphere, and there is already a tame sphere on the level that you summoned with the spell, the first one should explode. This would allow you to get them to “attack” monsters that they currently won’t attack.