Four expansion packs later, there are still some unsolved mysteries out there that plague World of Warcraft. DDGuides's here with 10 of them compiled into an entertaining video.
If you dig deep enough into various blue posts on the official forums and dev Q&As, you could probably find bits of information on these. But number two in this compilation -- what is going on with Tyr -- still remains a pretty interesting one.
Also, what about the remaining Old Gods?
10 Biggest Mysteries in World of Warcraft [YouTtube]