Question: "Walnuts & Rain" is an episode featured in which season of the American animated television series created by Pendleton Ward and featuring characters Finn and Jake?
Context: The second season of "Adventure Time", an American animated television series created by Pendleton Ward, premiered on Cartoon Network on October 11, 2010 and concluded on May 2, 2011.  The season was produced by Cartoon Network Studios and Frederator Studios.  The season follows the adventures of Finn, a human boy, and his best friend and adoptive brother Jake, a dog with magical powers to change shape and size at will.  Finn and Jake live in the post-apocalyptic Land of Ooo, where they interact with the other main characters of the show: Princess Bubblegum, The Ice King, Marceline the Vampire Queen, Lumpy Space Princess, and BMO. The ninth and final season of "Adventure Time", an American animated television series created by Pendleton Ward, premiered on Cartoon Network on April 21, 2017.  It is set to conclude sometime in 2018.  The season was produced by Cartoon Network Studios and Frederator Studios.  The season will follow the adventures of Finn, a human boy, and his best friend and adoptive brother Jake, a dog with magical powers to change shape and size at will.  Finn and Jake live in the post-apocalyptic Land of Ooo, where they interact with the other main characters of the show: Princess Bubblegum, The Ice King, Marceline the Vampire Queen, Lumpy Space Princess, BMO, and Flame Princess. "Walnuts & Rain" is the thirty-first episode of the sixth season of the American animated television series "Adventure Time".  The episode was written and storyboarded by Tom Herpich, from an outline by Herpich, Adam Muto, Kent Osborne, Jack Pendarvis, and Pendleton Ward.  The episode debuted on March 5, 2015 on Cartoon Network, and guest stars Chris Isaak as a bear named Seven and Matt L. Jones as King Huge. The eighth season of "Adventure Time", an American animated television series created by Pendleton Ward, premiered on Cartoon Network on March 26, 2016 and concluded on February 2, 2017.  The season was produced by Cartoon Network Studios and Frederator Studios.  The season follows the adventures of Finn, a human boy, and his best friend and adoptive brother Jake, a dog with magical powers to change shape and size at will.  Finn and Jake live in the post-apocalyptic Land of Ooo, where they interact with the other main characters of the show: Princess Bubblegum, The Ice King, Marceline the Vampire Queen, Lumpy Space Princess, BMO, and Flame Princess. The fourth season of "Adventure Time", an American animated television series created by Pendleton Ward, premiered on Cartoon Network on April 2, 2012 and concluded on October 22, 2012.  The season was produced by Cartoon Network Studios and Frederator Studios.  The season follows the adventures of Finn, a human boy, and his best friend and adoptive brother Jake, a dog with magical powers to change shape and size at will.  Finn and Jake live in the post-apocalyptic Land of Ooo, where they interact with the other main characters of the show: Princess Bubblegum, The Ice King, Marceline the Vampire Queen, Lumpy Space Princess, BMO, and Flame Princess. "Adventure Time" is an American animated television series created by Pendleton Ward for Cartoon Network.  The series follows the adventures of Finn (voiced by Jeremy Shada), a human boy, and his best friend and adoptive brother Jake (voiced by John DiMaggio), a dog with magical powers to change shape and grow and shrink at will.  Finn and Jake live in the post-apocalyptic Land of Ooo.  Throughout the series, they interact with the show's other main characters: Princess Bubblegum (voiced by Hynden Walch), the sovereign of the Candy Kingdom; the Ice King (voiced by Tom Kenny), a demented but largely misunderstood ice wizard; Marceline the Vampire Queen (voiced by Olivia Olson), a thousand-year-old vampire and rock music enthusiast; Lumpy Space Princess (voiced by Ward), a melodramatic and immature princess made out of "irradiated stardust"; BMO (voiced by Niki Yang), a sentient video game console-shaped robot that lives with Finn and Jake; and Flame Princess (voiced by Jessica DiCicco), a flame elemental and ruler of the Fire Kingdom.  The pilot first aired in 2007, and it was later re-aired on the incubator series "Random!  Cartoons" on Nicktoons Network.  The pilot eventually leaked onto the internet and became a cult hit on YouTube.  After Nickelodeon declined to turn the short into a full-fledged show, Cartoon Network purchased the rights, and "Adventure Time" launched as a series on April 5, 2010. The sixth season of "Adventure Time", an American animated television series created by Pendleton Ward, premiered on Cartoon Network on April 21, 2014 and concluded on June 5, 2015.  The season was produced by Cartoon Network Studios and Frederator Studios.  The season follows the adventures of Finn, a human boy, and his best friend and adoptive brother Jake, a dog with magical powers to change shape and size at will.  Finn and Jake live in the post-apocalyptic Land of Ooo, where they interact with the other main characters of the show: Princess Bubblegum, The Ice King, Marceline the Vampire Queen, Lumpy Space Princess, BMO, and Flame Princess. The third season of "Adventure Time", an American animated television series created by Pendleton Ward, premiered on Cartoon Network on July 11, 2011 and concluded on February 13, 2012.  The season was produced by Cartoon Network Studios and Frederator Studios.  The season follows the adventures of Finn, a human boy, and his best friend and adoptive brother Jake, a dog with magical powers to change shape and size at will.  Finn and Jake live in the post-apocalyptic Land of Ooo, where they interact with the other main characters of the show: Princess Bubblegum, The Ice King, Marceline the Vampire Queen, Lumpy Space Princess, and BMO. The fifth season of "Adventure Time", an American animated television series created by Pendleton Ward, premiered on Cartoon Network on November 12, 2012 and concluded on March 17, 2014.  The season was produced by Cartoon Network Studios and Frederator Studios.  The season follows the adventures of Finn, a human boy, and his best friend and adoptive brother Jake, a dog with magical powers to change shape and size at will.  Finn and Jake live in the post-apocalyptic Land of Ooo, where they interact with the other main characters of the show: Princess Bubblegum, The Ice King, Marceline the Vampire Queen, Lumpy Space Princess, BMO, and Flame Princess. The first season of "Adventure Time", an American animated television series created by Pendleton Ward, premiered on Cartoon Network on April 5, 2010 and concluded on September 27, 2010.  The season was produced by Cartoon Network Studios and Frederator Studios.  The series is based on a short produced for Frederator's Nicktoons Network animation incubator series "Random!  Cartoons".  The season follows the adventures of Finn, a human boy, and his best friend and adoptive brother Jake, a dog with magical powers to change shape and size at will.  Finn and Jake live in the post-apocalyptic Land of Ooo, where they interact with the other main characters of the show: Princess Bubblegum, The Ice King, Marceline the Vampire Queen, Lumpy Space Princess, and BMO.
Answer: sixth season