When does Tome of the Unknown return?

"Tome of the Unknown: Harvest Melody" is a 2013 animated short film created by Patrick McHale and produced by Cartoon Network Studios. The film serves as the inspiration and pilot for the miniseries Over the Garden Wall, which premiered in 2014. In the film, Wirt (Elijah Wood) and his brother Gregory (Collin Dean) head to the big city in search of an arcane book of all known things.