This one is more to encourage A/m hybrids, and it’s very simple:
We should allow some self-spells to be cast on enemy provinces. In particular, I’m thinking of Aggression, Bloodlust and Fanaticism; Mage’s Fury might also be a suitable candidate. Basically, the self-spells that have a drawback incorporated.
Why, you ask? Besides the encouragement above, I think it would add a level of strategy: should I weaken someone’s defense to get a hit with fanaticism but risk greater retaliation? Should I use bloodlust as a poor man’s Pitfalls and try to take out more units? Give us more, riskier options for spells, is what I’m getting at – other than Nightmare, maybe Mystic Vortex and (long term) Meteor showers, there is no magic way to reduce a target’s defense or take out their troops – and before you say thieves, they get Night Strike, maybe propaganda, and Bribe Generals, which is a fairly low-risk, low-gain affair.
P.S.: bring back Aggression as a support spell. It’s great for clearing out inactives.