My actor, a dragon priest, has a paralyze spell as part of his spell set, but he will never use it. Even if you give him only that one spell, it just runs away (unable to attack).

My overall aim is to have this actor be able to paralyze, and then drain the player. I used a normal human race actor originally with a custom shout. All worked great, just couldn't get the look I wanted. Changed to the Dragon Priest, and discovered that they can't shout.

Very frustrating.

Thanks in advance for any help.

Some have noticed if a spell doesnt do any actual damage it is usualy never cast. Custom spells created that do scripted effects etc never seam to be cast but when a 1 health damage magic effect is added the spell enemy AI will sometimes cast it. Try just adding a very minor damage magic effect to the spell and maybe try different NPC casters like warlocks etc.
Good luck let us know how you get on.

I presume you did adjust the AI Data Score? Sorry, I know that's a 'Did you turn your computer on?' issue, but just checkin'.

No need to apologise, as I honestly haven't a clue what you are asking, or where I would find it.

Coming mainly from MW (my oblivion modding knowledge is long forgotton), everything is insanely more complex and disorganised

I think I can now see what is causing the spell not to be used.

It's using ParalysisFFAimed Magic Effect, which has an alteration skill requirement of 75. My actor never has this so will not make use of the spell. I believe I'd have to either change my actors Class, or copy the Magic Effect to change the skill requirement.

Since my actor behaves like a vampire, but is a ghostly dragon priest, I'm going to try changing the class to match the vampires plus also make a low skill clone of the effect.

Just mod your actor to have a high alteration skill. ALSO: give your actor all the alteration perks.
I did that for one of my followers, and the first thing she does in every battle is cast paralyze at the enemy

It might also help to change the actor's combat style so they favor magic attacks over any other

Thanks. I'll try that.