Tome of the Unknown

"Tome of the Unknown: Harvest Melody", usually shortened to "Tome of the Unknown", 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—which is narrated by Warren Burton—Wirt, his brother Gregory, and Beatrice, a bluebird, head to the big city in search of an arcane book of all known things, meeting a vegetable man along the way.

Synopsis from Wikipedia, CC BY-SA 4.0. Everything below written here.