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21308 Adventure Time is a set based on the popular Cartoon Network series with the same name that was released in December 2016. This is the 16th set in the LEGO Ideas theme and the original idea was created by LEGO Ideas user aBetterMonkey. The set has 8 build-able characters from the show, Finn the Human with his original sword, Jake the Dog, Princess Bubblegum, Marceline the Vampire Queen with her axe guitar, Lady Rainicorn, BMO with a pair of joysticks, Ice King with his ice ninja throwing stars, and Gunter the penguin.
- The set was first shown off to the public at San Diego Comic Con 2016. Aside from this set, Adventure Time is also shown in LEGO Dimensions with the 71245 Level Pack and 71246 Team Pack. The 71285 Fun Pack featuring Marceline was also confirmed on a GameSpot E3 livestream by Arthur Parsons.