Greywolf1: I guess you have tried different variations of the Drain spell already, and confirmed that the game crashes reliably when you use it. And I don't think there are monsters or events which drain attributes in Arena.
If I remember correctly, there is a Transfer spell, but it works the wrong way (target -> caster).
You could hex-edit the attribute field if you can find it, I guess.
Well, stat draining *does* occur as a result of Disease or Curse, with the most well-behaved case being Disease inflicted by an enemy's attack.
I was able to get Willpower damage by using a Curse spell, however, it also damaged Intelligence, Personality, and Luck. I think I may try combining it with a Fortify effect to see if I can trick the game into thinking that my un-fortified stat is lower than it would normally be, and then rest to restore my other stats.
Curse spells don't behave as you would expect. In particular:
1. The spell only damages your stats once. You become immune to further curse effects until the current one wears off. (The Cure Curse does not appear to work properly, so it doesn't appear possible to end it prematurely.)
2. The amount of stat damage is equal to the value of the Y value of "X rounds per Y levels", so if I set the duration to 1 round per 20 levels, the affect stats decrease by 20. (Note that this parameter does not affect the duration as it should; however, increasing it *does* reduce the cost.)
It seems the programmers did not actually test some of the more obscure and less useful effects as they should have. (This isn't the only bugged effect: Cause Disease seems to either do minor Intelligence damage over time or kill you in 5 seconds, for example, while Continuous Damage is weaker than it should be but lasts forever.)
Edit: My idea about using a Fortify effect worked. So, the trick (for lowering stats affected by curse) is as follows:
1. Inflict yourself with a Curse. The duration should be set to 1 round per 20 levels (which actually gives it a magnitude of 20).
2. After your stats drop (you will notice your magic meter get fuller when this happens), use a Fortify Willpower (or whichever stat you want to lower) spell. The magnitude can be as low as 1, but the duration should be long enough to rest to heal the stat damage.
3. Rest until your stat damage is healed. The Fortify spell should be in effect.
4. Wait for the Fortify effect to wear off. Fast Travel will work for this purpose.
5. Your stat has now been lowered, and will remain at the lower value until you rest.
So yes, it *is* possible, but is more cumbersome than it should have been, and is definitely not how things were intended to work.