Nightmare demon begs for a reference to Sebastian's belt:
Inquisitor: That thing's...you know has its own face!
Varric: I knew a guy with the same problem.
As for the designs that's some real H.R. Giger stuff they've got going on. Bloodletters of Khore, Screamers of Tzeench, and even Nurgle's Plaguebringers I can deal with. These make me think of how freaked out the first time I watched Alien as a kid (which admittedly wasn't the best idea at the time).
Sebastian was my first thought too! 
I think they've done an amazing job with the demons, really. Very "We have such sights to show you." *shudder*
I can poke fun now, but when I'm playing I'll probably be doing what I did when I first saw what was waiting in the tower of Ishal, which went sort of like this: "What the...no no no no NO NO NO NONONONONONONO" as it headed right for me. And these are far scarier than an ogre. I'm just glad I'll (hopefully) have my companions with me, because I don't like fighting things like this solo, especially when they're sneaking up on me in the dark. It's why I don't play horror games. I'm basically a giant chicken.
Which is why I STILL can't watch Alien.