I like the idea of having themes with the suits that you were talking about, and I must add I am really diggin that creepy underwater multi-eyed dude with pokey spines! An underwater theme would be awesome.
I'm pretty sure you have the cutest demons in the class. I like the idea you play with having just the demons back being shown, leaving more to the viewer to assume what is happening. Imagination is usually creeper then what can be depicted.
I told you already that the multi-eyed slug creature was one I was really enjoying. I especially like the suit of legless creatures. The other ones are fun designs that I think will mesh well, too.
Yep, the big head demons are pretty cute. I dig the idea of big heads, floating torsos with arms and sadly, I forget the specifics of the others. I agree with Josh. I think having some demons with their backs to us or submerged in shadows might make them creepier. That having been said, however, I think the most original demon you have is the pogo-stick demon. Think about how many kids probably get hurt on pogo sticks. I think it would be really interesting if you explored "potentially harmful" gadgets or devices as a universal theme. You can still have big head guys and floating guys, but a universal theme would give them context.