Here's how the family behind the indie video game 'Cuphead' sold 3 million copies without any formal training in game design

Even as they cared for young children, the Moldenhauers dedicated themselves to creating "Cuphead" from scratch.

Marija left a corporate job to help manage the project, and eventually started helping with the game's art and animation. Marija and Chad contributed hand-drawn cells for animation while James led the gameplay design.

"Cuphead" is a living homage to 1930s animation, with a big band musical score to match.

The game plays like a mashup of classic titles like "Contra," "Mega Man," and "Super Mario World," with players running and shooting their way through dozens of challenging bosses and stages.

The Moldenhauers say the game has set world records for the most boss battles and boss transformations in the run-and-gun, shoot-'em-up genre.

The video also revealed that "Cuphead" holds a record for the most hand-drawn frames of animation in a video game, with more than 45,000 cells. Caitlin Russell, a background artist and painter for "Cuphead," said that each background has between seven and 11 layers, and single screens like the one above can take about a week to complete.

"I don't think we would have been able to put in the hours and effort that we did into it, unless it was purely a labor of love," Marija Moldenhauer told Red Bull.

Studio MDHR isn't done with "Cuphead" just yet: In 2019, the game will be getting an update called "The Delicious Last Course" that will add a new playable character, Ms. Chalice.

You can find "Cuphead" on Xbox One, PC, or MacOs, and Studio MDHR is promising more games for the future too.