Argentinean director Andres Muschietti adapted his short film "Mamá" into this eerie shocker. Lucas and his girlfriend Annabel take custody of his two young nieces who've spent the five years since their parents' deaths living in an abandoned cabin. Their only companion was an imaginary friend they call "Mama." But Mama is anything but imaginary. She's actually the ghost of a 19th-century mental patient and she's claimed the girls as her own. Jessica Chastain, Nikolaj Coster-Waldau star.