An open world video game for the TV animation, Adventure Time. Ideas from members of the Adventure Time sub on Reddit: Reddit Post

Explore the Land of Ooo and all its inhabitants, dungeons, and kingdoms. Play solo or online with others. Choose a character, or create your own. Advance your character(s) to gain favorable attributes and powers to help you explore the very distant land and waters of Adventure Time. Play missions, side missions, and mini-games from and with various characters seen on the show. Build your own treehouse and upgrade it using all your precious loot. Gain favor with the characters that you interact with to earn character exclusive items. 

Possible expansion ideas: Lumpy space, the nightosphere, the crystal dimension, the underworld, the multiverse, Mars, warren ampersand’s dimension, pillow world, pre-apocalypse, much more.