Which animated short film created by Patrick McHale was Over the Garden Wall based on 
Over the Garden Wall:  The show is based on McHale's animated short film "Tome of the Unknown", which was produced as part of Cartoon Network Studios' shorts development program. Tome of the Unknown: Tome of the Unknown, the full title of which is Tome of the Unknown: Harvest Melody, is a 2013 animated short film created by Patrick McHale.
Tome of the Unknown