The more difficult quests in RuneScape. While Guthix Sleeps, The Chosen Commander, A Clockwork Syringe (also full to bursting with Crowning Moments of Funny), King of the Dwarves, The Void Stares Back, the Mahjarrat quest series.
To elaborate on the Mahjarrat quest series, the predecessor to the current god of chaos, Zamorak, was a god called Zaros. Now, Zaros used baddies like the Mahjarrat (dudes from a plane of eternal warfare), vampires, demons, etc. Also, he was the worst enemy of Sarasomin (god of order, usually depicted as good), and his empire covered most of the world. It was bad enough that Saradominists helped Zamorak defeat him, and later would ally with Zamorakian forces to destroy Zarosian forces, sites, etc. Basically they really wanted to wipe all trace of him off RuneScape. All of this comes like 5 years before the Mahjarrat quest series even started.
So he sounds like a pretty bad guy, right? The general consensus was that he was the god of evil.
Now, 5 years later, this new quest series about the Mahjarrat comes out, and points out that nothing actually strongly points to him being evil, and his alignment is a total mystery. Also he's not as dead as everyone thought, we get to communicate with him, and the next Mahjarrat quest probably has us trying to bring him back to godhood. While preventing another from attaining it as well (different quest line converging.)
To put this into perspective, this is the equivalent of Blizz having the foresight to set up draenei lore in Warcraft 3 so that the introduction of the draenei into the Alliance in WoW would make sense without a retcon, while still being totally out of the blue.