Shadow of Israphel is the third and final season of SoI, and comprises the bulk of the Israphel mythos. It follows our heroes in their epic quest to end the reign of Israphel and save Minecraftia from his wrath.
For more info, see the Yogscast Wiki.
This is probably where the bulk of SoI Fanon will go. If so, remember to read up on the series and follow the story editing policy.