So what's behind Monster High's out-of-this-world growth?

One factor is Mattel's identification of a more mature doll consumer. Where Barbie used to be marketed to any girl before her teenage years, the doll now has greater appeal among those under 6. What Mattel saw, and took advantage of, was a niche in the market -- a doll for the girl who had outgrown Barbie but not yet grown into Twilight.

Then, Mattel created a world. It realized the way children consume had changed and adapted to suit. Where the physical product used to be enough to garner sales, now it's about creating a rich tapestry, a backstory to kick-start the imagination.

As a Mattel spokesperson put it, "Fish where the fish are feeding." If children are on social media, watching YouTube and playing online games, upload branded content, have them chomp at the bit to play with the next big toy and then introduce it to shelves. Rinse and repeat.

"Storytelling is and will always be the anchor of Monster High's connection with girls. We continue to engage with fans through our entertainment and content initiatives," Stephanie Cota, Mattel senior vice president of global marketing, told TheStreet.

Mattel's Monster High-branded online content has garnered more than 540 million video views (both via and YouTube). Monster High's theme song, Fright Song, has been downloaded more than 1 million times (for 69 cents, no less). Then there are the branded backpacks, costumes, books, video games. This is a formidable empire.

"We're able to reach girls everywhere they are today -- online and offline," said Cota.

There's also its extendibility. Monster High attended the Pokemon school of marketing: "Gotta Catch 'Em All!". With no foreseeable limit to how many monsters and legends Mattel can appropriate (you've got to assume werewolves have a litter of at least five), it's an unlimited supply of future sales.

Of course, Mattel isn't slowing down in its complete domination of the fashion doll category. Recently launched Ever After High has a similar strategy to Monster High. Where the latter is all spooky and scary, the former borrows from Disney-fied Grimm Brothers stories, with dolls such as Apple White, daughter of Snow White, and Madeline Hatter, daughter of Lewis Carroll's Mad Hatter. The line had a strong debut at Justice stores in the U.S. during the third quarter and Mattel is currently rolling the brand out to major retailers in 14 markets globally.

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