Want to know: The Harrowing

So, its been confirmed that the Hecarim, Zed, and Twisted Fate splash art changes are for The Harrowing, along with the smoke on these splashes and a few others. But, what exactly is happening? Is there going to be something awesome on Halloween? A new champ? Skin? Anything?

Just curious to see what everyone thinks. Ive already heard theories that its Ao Shin's champion preview and that its a Shaco ultimate skin, but what else does everyone have to say about this whole thing?