Here's a subject of debate:
Up to this point we've had three or four cliffhanging details at the end of a couple episodes.
What do you think they might mean? Are they all connected or will some/all be independent? And what might they be related to?
1) The shadowy figure in the Castle of the Royal Sisters (Castle Mane-ia)
2) Disappearing enchanted comic book (Power Ponies) ... (i dont believe it means anything, but others might)
3) Fluttershy's vampire fruit bat tooth (Bats!)
4) Flashy Rainbow spool (Rarity Takes Manehatten)
We don't know what they are for or how important they really are. It can be assumed that 3/4 will have a return at some point for some reason. What are your ideas?
I believe the Shadow Pony is quite likely a secret villain to be revealed in the finale, possibly even spoken of before then but subtlety enough to not arouse suspicion.
Fluttershy's bat tooth mostly likely means she retained some of the vampire fruit bat DNA, I'm going to assume nothing will be seen about till the finale when something forces her back into that form and she will somehow lose it entirely (might be the finale, might be prior).
It is possible that they're using the word "key" metaphorically, and that they won't physically appear to be keys until the finale. In which case, the spool of rainbow yarn is probably one of them. And as for the enchanted comic book disappearing, I don't think it is related.
I'm still hoping they find some actual "physical" keys to unlock the box. It seems more interesting to know "okay girls, we've got one key. now to find the other five!" than finding out at the finale they had the six keys all along.