So I have a scroll that is scripted and conditioned only to work on Vampires. How can I make the NPC understand not to waste it on opponents that are not vampires?

The only thing I can think of so far is to remove the item from their inventory if their combat target is not a vamp.

Solved this with an old Oblivion moding trick I used often, by removing the health damage from the spell itself and moved it to the script.
Now the AI sees the spell as almost harmless and picks some other way to attack instead.

I really wish we had more options in the combat AI to handle this kind of NPC decision making instead of using these kind of tricks.

you can put a condition in the spell where it links your magic effect so that it will only fire the magic effect if the condition is met

err... huh?

How would that stop the NPC from trying to use the scroll? Maybe I do not really understand what you are saying (I am a little sleep deprived and my head is a little fuzzy) but if you mean to condition the spell magic effect, then yes this would stop the spell but not the use of the scroll (the scroll would still be used and waste the attack round and the scroll).

If you're just worried about wasting it, why not just script the effect to add another if the conditions are wrong? It wouldn't solve them using it, but at least it would stop them just vanishing when used...

Stopping them from using it is half of the issue. They will waste many attack rounds doing so over and over and over again if I just replace the scroll in their inventory. And as I have said, I have cracked the solution already using some old oblivion moding slight of hand.

I just wish Bethesda had allowed skyrim combat moding to be as flexible and powerful as the magic moding can be. More accessibility to the combat AI would help a lot.

OP requested close.