Re: When casting remote attack spells...
 

true, horrors could take you out immediately, and they have high MR.

If however you can enslave them all and survive then the forbidden light has another advantage

(catching horrors to temporarily fight for you ain't bad, so they go away after some time - oh well)

offcourse the question is even with all that penetration Can you enslave them?

Re: When casting remote attack spells...
 

Even a Lesser Horror has MR18.

Penetration +11 works out to +7 with Master Enslave, so MR18 versus 17.

You could add 2 pearls for 1 more penetration, but you're going to be at 200 fatigue after casting no matter what. So, 50% likely you're going to die, and that's only if just one shows up, and if you actually cast what's scripted, instead of Astral Shield or something.

In any case you're spending 10 pearls a turn enslaving horrors.