Guillermo del Toro presents Mama, a supernatural thriller that tells the haunting tale of two little girls who disappeared into the woods the day that their mother was murdered. When they are rescued years later and begin a new life, they find that someone or something still wants to come tuck them in at night.

As a producer, Guillermo del Toro (Pan's Labyrinth, Don't Be Afraid of the Dark) has a knack for coming up with projects that are not only original, but extremely frightening. Mama is no exception, providing a uniquely terrifying experience.

The opening of Mama sees a man named Jeffrey (Nikolaj Coster-Waldau from "Game of Thrones") murder his wife, kidnap his two daughters and run away to a secluded cabin. He is about to kill both of the girls and himself, but is stopped by...something. Five years later, Victoria (Jennifer's Body's Megan Charpentier) and Lilly (Isabelle Nélisse from Whitewash) are discovered in the cabin, completely neglected but claiming to have been taken care of by "Mama." A psychologist named Dr. Dreyfuss (Daniel Kash from Aliens) places the girls with their uncle, Lucas (also played by Coster-Waldau), and his girlfriend, Annabel (Zero Dark Thirty's Jessica Chastain). The girls move in with Lucas and Annabel, but Mama has come, too. And she won't let go of them as easily as Lucas and Annabel would like.

Mama is based on the horrifying short film "Mamà" by Andrés Muschietti. Guillermo del Toro had Muschietti (now calling himself Andy), along with his sister Barbara Muschietti and television writer Neil Cross ("The Fixer"), expand the short into a full length screenplay by creating a believable backstory and fleshing out the unanswered questions in the short. Mama adapts well into a feature length production; whereas the short is pure adrenaline terror, the feature gives the audience time to breath and soak it all in, letting them relate to and care about the characters - and then it scares them to death.

The tension in Mama is unfathomable. Mama shows herself to the viewer little by little in a perfect reveal, and the suspense is maddening. For example, in one scene, Annabel notices that the closet is ajar. She approaches it, and Victoria tells her not to open it. She pauses, letting the viewer think that she's going to look inside...then closes it. The Mama doesn't even have to show her face to make the viewer uncomfortable, and Mama is full of moments like this.

Of course, Mama doesn't always stay hidden. She is one of the most frightening characters in recent horror memory. She's a shape-shifting, slippery menace that terrorizes anyone and everyone who threatens Victoria and Lilly. And Mama's got one heck of a jealous streak, one that Annabel learns about first hand when Victoria takes a liking to her. The Mama in Mama is not one to be messed with.

The only thing that keeps Mama from getting a fourth clock is the ending. The screenplay succumbs to a common horror movie trend; it tries to humanize its antagonist. Of course, like any horror villain, Mama has an origin story. Mama's story, however, weakens her character. The third act tries to elicit sympathy for her, but all it does is soften the climax. What should be a balls-to-the-wall battle with Mama ends up...not. The film is still very watchable and will scare even the hardest of the hard, but the ending of Mama falls short of expectations.

A big part of what makes Mama such an effective horror film is the visual effects that are used to bring the Mama character to life. Mama is a combination of Spanish contortionist Javier Botet (who also played the creepy Niña Medeiros in the [Rec] films) and some slick CGI by DDT SFX and Mr. X. Inc. Botet portrays the actual movements while the effects add a ghostly, otherworldly appearance to his performance. The positions in which Botet puts his body are downright freaky, and the post-production animation makes Mama do things that should not be done; like scuttling across a ceiling or disappearing and reappearing somewhere else. Having an actor play the title role gives the other characters something to play off, so their performances are more convincing as well. The hybrid practical/CG method of bringing Mama to life works in its entirety.

The cast in Mama is great. Of course, the adults do their jobs; Nikolaj Coster-Waldau is good in his double-duty role, Daniel Kash is an effective Dr. Dreyfuss, and Jessica Chastain is remarkable in her reluctant maternal role of Annabel. However, the real show-stealers in Mama are the little girls. Megan Charpentier's Victoria is both articulate and intelligent without losing her little girl charm, and Isabelle Nélisse plays her part of Lilly perfectly, one chilling half-smile at a time. Both girls have bright futures, and hopefully both keep making horror films.

Mama is scary on a few different levels. The character herself is just eerie, moving between the astral and physical plane at will and doing anything to protect the girls, even when they are not threatened. Mama's ability to creep and crawl around builds suspense and tension; the audience sees her slipping and sliding about, but does not know where she'll strike. Mama is also full of jump scares, some cheap and some legitimate, but all effective. Mama brings the viewer to the edge of their seat, makes them jump out of it, then follows them home and hides in their closet.