This short is essentially a proof-of-concept for what would become Over the Garden Wall, a fun mixture of fairytale tropes and classic 'Silly Symphonies' type cartoons. The show is thankfully more well polished, but this was a fun, rough outline for where it was going. I'd recommend this as a fun bit of 'bonus content' if you've finished the series and still want just a little bit more.
Review of Tome of the Unknown
