Ten year old Ruby Gloom, the happiest girl in the world is visited by her parents, Sam and Audrey Gloom whom she hadn't seen for same time. But when a cruel Wendigo known as Daemon appears, Ruby' mother was lost and after that Sam has Ruby transferred to an all girl private school where she meet and befriends three girls named Tracey, Hazel and Cloris.
- Dakota Fanning as Ruby Gloom, a happy ten old girl who always looks on the bright side.
- Kristan Stewart as Misery, a very misfortunate banshee-like girl.
- Ellie Fanning as Tracey, a school girl who becomes a close friend with Ruby Gloom.
- Andrew Garfield as Skull Boy, a living skeleton.
- AnnaSophia Robb as Iris, an adventurous darting cyclops.
- TBA as Cloris, a young toddler girl and new friend of Ruby
- Tommy Lee Jones as Samuel "Sam" Gloom, Ruby's father.
- Martin Short as Scaredy Bat, a vampire bat who's pretty much fears everything.
- Gabrielle Aplin as Doom Kitty, Ruby Gloom's pet cat.
- Greg Ferguson as Poe, a raven and rhymester, who is named after the famous poet, Edgar Allan Poe.
- Justin Timberlake and Lance Bass as Frank & Len, two male dicephalic humanoid conjoined twins who love to be rockers in nature
- Emma Watson as Audrey Gloom, Ruby's mother and Sam's wife. She is tragically killed by the beast known as Daemon.
- Bailee Maison as Hazel, a tomboy and new friend of Ruby.
- Rebel Wilson as Principle Hicks, head of Hicks' school of Girls.
- America Ferrera as Pearl Bitterman, a school bully.
- Mr. Buns, stuffed toy rabbit.
- Daemon, a demonic Wendigo-like creature.
- Falling Night Sky: Performed by Gabrielle Aplin.
- A Gloomy day in Gloomville: Performed by Dakota Fanning.
- Thank you Ruby: Performed by Justin Timberlake and Lance Bass.
- Within your heart dwells a soul: Performed by Gabrielle Aplin.
- Beware Daemon: Performed by Greg Ferguson.