It was written by Josh Weinstein, Matt Chapman, and Hirsch, and directed by Sunil Hall, and originally aired on Disney XD on July 13, 2015.
Before federal agents locate the portal, Grunkle Stan takes the time to reveal his past to Dipper and Mabel, along with the secrets of his brother Ford.
In high school, Stanford built a perpetual motion machine poised to grant him entry to his dream college across the country.
With the help of his college friend Fiddleford McGucket, he built a universal portal that could lead to the home dimension Gravity Falls’s anomalies originated from.
Plagued by guilt, Stanley spent the next thirty years attempting to re-activate the portal, which he only accomplished recently after finding the other two journals.
To make ends meet and develop a cover story, Stanley assumed Stanford’s identity and faked his own death, turning his brother’s old house into a tourist attraction: the Mystery Shack.