What is your favorite WoW mystery?

Before Cataclysm hit, I feel like there were a lot more true mysteries in the game. Cata removed a lot of that, but some remain. One of my favorite things to do used to be watching videos on that sort of thing or reading old threads, there was a giant one on mmo champion.One of my favorites was the friendly naga zalashji. He patrolled the coast of tanaris. He had no interactions, but would occasionally roar in the direction of the sea. Many people tried all sorts of crazy ideas to interact with him to no avail. People submitted tickets asking what he was for and the answers ranged from the players haven't discovered yet, an old quest that was removed, nothing, something but they aren't allowed to give hints. Anyway, when cata hit he vanished and a cave was named after him, zalashjis den. I don't think to this day anyone truly knows what he was for.Other favorites were legends of the ashbringer which i suppose have been solved with legion. What is under tirisfal?So what is yours? Even if it's been solved or lost to revamps.