love the way you handled the unicorn thing... the problem with stories like this is that it always makes me think 'out of all the people that are connected to Hogwarts, Muggleborns and their parents included, why did no one ever come up with something like that?!'
so I hope you go for option 2 or otherwise I'll drive myself crazy from frustration :-P
I take it Dumbledore has arrived and sent that spell? first Snape almost kills Harry, then Dumbledore... do those people not look before they cast spells? or at least get the innocent bystanders out of the way?
some people really need to be replaced... though I'd prefer if it wasn't done maliciously: like Snape going to Azkaban or something like that. while I don't think he should ever have been a teacher, I rather like him as a character.
I too like tearing down plotholes (like the schedule... no way could one teacher teach all those classes!) but I also like arguing about them.
mind some arguments on the challenges? otherwise skip to the end of this review.
the teachers never came down there as far as I can tell. Hagrid fed Fluffy but other than that is was undisturbed. all the teachers only knew their own challenge so they couldn't have gone past the others. that was probably a safety precaution so what the challenges were couldn't be weaseled out of one single person so I doubt Dumbledore would let ANYONE down there.
it's possible that the chessboard reset itself once people leave the room... only since Ron never left it never reset itself. Dumbledore probably had an override or something like that... he'd have made sure he could get across the challenges quickly. as for the flying over it...
I'm not sure how close the board and the pieces were to the door (no I haven't seen the movies) so I'm not sure it'd have been possible to fly over it to the door. And if stones can be animated and move around, why wouldn't they be able to jump?...
I do like what you've done with the challenges though... I still like Snape's best...
hope you'll continue soon!