Garett Bobby Ferguson and his son, Garett Bobby Ferguson Jr. awaken from hell and escape, ready to wreak havoc on the Park. Mordecai and Rigby must gather their friends to help defeat the duo, but GBF hypnotised all the park groundskeepers and their friends and created a bunch of new monsters called Yummies, so Mordecai and Rigby must defeat their friends and evil Yummies to un-hypnotise them with their tamed Yummies and collect seven jewels (The Seven Star Jewles) to defeat GBF and GBF Jr.