This goes without saying, the concept is pretty cool but the execution is lacking.
I requested some changes on another thread, but here is what I think we need.
1. Debuffs require line of sight to to cast
1A. Debuffs cannot remain active for more than 4 turns after line of sight is lost.
2. AI must actually have enough mana to maintain Debuff spells.
3. There needs to be an indicator in Cloth view that a debuff as well as buff is on a city. -Maybe spell icon and counter if more than 1 of that spell is active.
4. to offset the fact that we can now see it - counter spell takes 2 turns to clear debuff - or maybe a little more mana.
* Debuffs should require that you have seen your target at one point. Most spells should actually require active LoS excepting very special cases. AND then you have a reason to create a spell which allows you to see everything you have explored (more spells, YAY!). I have absolute proof that they will cast debuffs on cities they have never seen. I had 9 Incinerate cities before I had even made contact with another empire (wildlands cut me off, which was actually pretty awesome).
* Debuffs should REMAIN after cast regardless of LoS so long as you choose to continue paying upkeep. Requiring LoS for debuffs to continue would just make them useless in all but siege situations. They should be a way for a military weak but mana strong empire to weaken an oppressor.
* If AI is deficit maintaining their magic we have a problem. That should never be.
* Not only should there be better indicators that debuffs are on a city, I want to know when one is cast. These are ATTACKS. You don't let them wipe an army without notifying you. Why do they get to cause a permanent debuff (-hps, no dispel) to my trained units without me knowing? Frankly, I intensely dislike that mechanic in general, but if that's the intended design, whatever.
* Counterspell should probably cost 40-50 mana, but the fact that you don't get to choose what you are disenchanting is a negative. It is a defensive spell. It should be acquired relatively early, be easy to identify (it currently is not), and fairly quick, if spendy, to utilize.