There are 3 plates on the rooms you described. One of them you can mantain pressed with an object, but I don't know what it does. the other two makes the south-central demon head shot lightning bolts. There's also a demon head on the west side with no hole to get the bolt at the end. I noticed that sometimes the central head shots a different ray, that makes the pit on the top-center close but it's a fast event. The problem is I found the bolts too random, and thy even stop randomly.If you can point me exactly what to do with tis room I´d be grateful.
I hope the goromog don't mess my entire game, since I need a key he possess. Tried to kill him several times, with my heroes with full strenght but got no luck.
Also, this central room with the crabs is still a mystery, I can't see how to access it now. Abouth the big puzzle you mentioned, I hope I can figure by myself once these problems were gone.
But I have to tell, you did a hell of a job with this module, so far it's the more balanced I played, and the best. I hope I can still continue it till the end.