Not to spoil but take a look at this teaser first:
Star vs. the Forces of Evil: The Battle for Mewni is an upcoming two-hour television movie for Star vs. the Forces of Evil.
It is scheduled to premiere on July 15, 2017 and will be available to verified users on the Disney XD app and Disney XD VOD platforms.
The TV movie follows:
Star as she returns to her home dimension of Mewni where she discovers that magic is disappearing throughout the kingdom. Star must dig deep and challenge archnemesis Ludo in an effort to save her family and kingdom
*This will be the second Disney XD animated movie since Phineas and Ferb The Movie: Across the 2nd Dimension.
*According to Daron Nefcy, the film makes up the first four episodes of season 3