New spells.

Create your own spell with the help of a mentor, and you'll be happy! In the final battle, I cast Subjugation (without it, I don't think it's possible to complete the mission; at least, I wouldn't be able to), Divine Retribution (a super-mega thing that dealt over 10K damage; a Warlock can only dream about it), and finished off the stacks with Earth Shock. I didn't use Summon at all; the Shield and Phoenix were destroyed with one hit. But about the wall... I didn't even think about it! But it wouldn't have saved me from the devils anyway.
P.S. And Subjugation seems to work on Nightmare Devils...