Lonely and emotionally fragile, teenager Casey (an excellent Anna Cobb) lives her isolated life largely via the Internet—specifically, through the “World’s Fair Challenge,” an immersive online horror game that promises body modifications and personal tumult. As she falls deeper into its grasp, Casey feels her grip on reality slipping, bit by bit. Part experimental unease and part heartbreaking character drama, writer-director Jane Schoenbrun’s unique look at modern-day interpersonal dynamics is a genre-blurring marvel. —Matt Barone