"Is Mystery" is the second segment of the twenty-third episode of Star vs. the Forces of Evil. It premiered on October 3, 2016 alongside "Friendenemies", and is the second segment of the tenth episode in the second season.
Worried about his tadpoles’ futures, Buff Frog investigates the hole in the Mewman force field.
- Star Butterfly and Marco Diaz are both completely absent for the first time, but Star is mentioned by Buff Frog at the end of the episode.
- October 27, 2016 (United Kingdom and Ireland)
- November 18, 2016 (Italy)
- January 13, 2017 (Poland)
- February 12, 2017 (Japan)
- March 8, 2017 (Latin America)
- April 21, 2017 (Southeast Asia)