Gravity Falls Gravity Falls

Perhaps Richard Castle can solve the spooky mystery of Gravity Falls. On Monday's episode of the hit Disney XD animated series, Castle star Nathan Fillion makes a guest appearance.

Fillion plays Preston Northwest, the father of local tween Pacifica — who's an archrival of Mabel Pines (Kristen Schaal). In the episode "The Golf War," Mabel challenges Pacifica to a rousing game of miniature golf. Things get out of hand, however, when a group of local residents — the Lilliputians — offer their help. Also guest starring is Patton Oswalt (The Goldbergs) as Franz, one of the Lilliputian leaders.

Grunkle Stan, Dipper and Mabel Pines returned to Gravity Falls for a second season. A mix of Twin Peaks, The X-Files, Lost and Scooby Doo, the mysterious world of Gravity Falls was created by Alex Hirsch. Hirsch, Jason Ritter, Kristen Schaal and Linda Cardellini star.

"The Golf War" airs Monday, Aug. 11 at 9:30/8:30c. Here's a first-look at the episode.

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