During high school, Mordecai and Rigby wanted to go to "College University" together, but Rigby did not get in. Frustrated at his friend being accepted, Rigby changed Mordecai's acceptance letter to say that he was rejected. To get accepted, the two finish their Science Teacher's time machine to tell their past selves to get better grades. However, they explode the science lab, resulting in both of them being expelled and unable to go to "College University". Mordecai went to Art School while Rigby, who did not graduate high school and therefore did not go to college, stayed in his dorm, until Mordecai dropped out.
For awhile, a goat-intern named Thomas was in the park for "school credits", however, on his last day of his 2-year internship, he was revealed to be a Russian spy who wanted to steal the park. This almost happened, but didn't. As of then, Thomas has been on the run, but has still met up with the park workers a few times: at weddings, parties, and other various reasons. Mordecai has several romantic storylines throughout the series. He used to have a crush on a robin called Margaret but after she moved to a far-away college, he became depressed for awhile. He later got over it and then dated a cloud girl called CJ, who he had met previously. However, Margaret returned from college to work at the news station and ended up having a few incidents with Mordecai, making Mordecai and CJ break up at Muscle Man's wedding with his wife, Starla.
In the earlier seasons, Rigby used to dislike Eileen, a mole who had a crush on him, but they start dating a couple of months before Muscle Man's wedding. In the episode "The Eileen Plan", Eileen shows a list to Mordecai, Rigby and Margaret that details all of the things she wanted to do before she turned 25, all of which she now views as a joke. Rigby is upset to hear that Eileen wanted to marry a smart man, so he goes back to high school to pass science, foreign language, and Phys. Ed. class.
During his return to high school, a dome is placed over the park, and once Rigby had graduated, the park gang, alongside Eileen, were sent into space for a mission. During this time, Pops is revealed to be the "key to the universe", and that he must fight his evil twin brother, Anti-Pops, on his home planet of Lolliland in order to keep the universe from being erased. Pops does this but ends up deciding that love is more powerful than fighting, so after Anti-Pops kills all of Pops' friends aside from Mordecai and Rigby, Pops hugs his brother and flies into the Sun, killing them both and reversing everybody else's death. The park then returns to Earth after three years of being in space. Mordecai reunites with his parents, Rigby reunites with his parents and Don, Benson reunites with his pet pig, Apple Sauce, Skips reunites with Techmo, Muscle Man reunites with Starla and discovers that he is now a father, and Hi Five Ghost reunites with Celia. Mr. Maellard is upset about Pops' death.
Twenty-five years later, statues of both Pops and his late father are built in the park to remember them. Everybody, apart from Skips and Benson, have left the park. Mordecai is now a successful artist, and has found the perfect woman, a bat-girl named Stef, whom he has married, and has three kids with. Rigby has married Eileen and now has two children. Benson still works as the park manager, and is now married to one of the dome scientists, named Pam and now has his hair back and still owns Apple Sauce, and four cats. Skips is still the same, but he now wears shorts. Muscle Man and Starla have six more children, who all follow his dirty traits. Hi Five Ghost and Celia move to Prague in the Czech Republic, becoming successful DJs together, and also have a son together. The series ends with Pops watching it in heaven, calling it a "Jolly Good Show".