Sesame Street: Once Upon a Monster lets gamers join the Muppets as they enter a living story book entitled Once Upon a Monster. In the book players will make new friends with the Muppets and go on adventures with them while solving problems and learning new life skills along the way. The game will allow players to control Elmo and Cookie Monster as well as a new character named Marco. The focus of the game will be mini games that make the player move to avoid obstacles or help their fellow Muppets reach certain items, as well as dancing.
During the development of Double Fine's most recent retail release, Brutal Legend, Tim Schafer decided to create an "Amnesia Fortnight", splitting the company into four different groups and over a two week period have each group come up with a game concept and pitch. What became Sesame Street: Once Upon a Monster was one of the titles pitched at the end of that fortnight, along with Costume Quest, Stacking and Trenched.
The prototype was led by Nathan Martz, with his vision being for a game inspired by the Muppets and Sesame Street - with monsters singing and dancing. After the announcement of Kinect, the team found it a natural fit for the game and decided to incorporate it.
After demoing the game to a number of publishers, WB Games signed on to publish the title. At the same time, WB Games signed a deal with Sesame Workshop to create Sesame Street games, and knowing this - Double Fine pursued for the licence.
This required some minor changes to the game, several monster characters were either dropped or changed, and the characters of Elmo and Cookie Monster were introduced.
Sesame Street: Once Upon A Monster was released October 2011.