AI and Spells
 

I am working on a mod where I plan to add and change some of the existing spells. How will AI handle that? How does the AI decide what spell to cast in combat and on province basis and global spells?

Re: AI and Spells
 

On combat, the AI compares how effective various spells would be (how many creatures they would affect, how much damage they would deal, total). There's also some kind of priority modifier that makes some spells more likely to be cast. I don't know if that modifier is calculated automatically for new spells. I have no idea how the AI chooses ritual spells.

If ritual spells also use some kind of priority mechanic that makes AI favour some of them, it wouldn't be that hard to make the AI prefer good summons instead of crappy ones, avoid summoning Harvesters of Sorrows etc. It'd be a lot of work to go through all the spells, of course, so it could be that this wouldn't happen even if we had the capability.