A Final Epic Adventure is the series finale as well as the one-hour long special and the twenty-seventh episode in Season 8 (and two hundred and forty-fourth overall) of Adventure Time.
An epic final battle begins and concludes, all deciding the fate of the universe. The park crew arrives at Lolliland, the place of birth of Pops and Anti-pops. The place is all shattered of all the old fights the two brothers had and there they meet a group of natives from Lolliland, Frivola-Kranus, Quadravi-Kranus and Weird Mushroom Guy, they tell the crew of the previous battles Pops and Anti-Pops had, also they discovered Pops real name, Mega-kranus and Anti-Pops', Malum-kranus, and how the lolliland natives have been evolving to the point Pops was born. In the ancient tapestries show every battle ever done, and there is a section where warriors resembling the park crew are fighting along Pops, meaning they were meant to fight in the ultimate battle, but now that they know that they are meant to end the fight in a stalemate, Mordecai thought of setting traps for Anti-pops so they get an advantage in the battle, Pops was against cheating but he was also convinced that they have to win to save themselves so he helped them to set the traps.
Anti-pops arrives in a Uber-like driver, Pops still tried to convince him to not fight, but Anti-pops refused, after singing the Lolliland anthem, Anti-pops started the fight but everyone had striked him with the traps, at first they were excited about defeating Anti-pops but then he returned unharmed from the traps, Pops still wanted a fair fight, so they made a deal of who ever knock the other first, can do what they want to the universe, they both agreed and started to fight, which in the first round Pops crushed Anti-pops with a cruise boat, but Anti-pops broke the deal and continued the fight while the park crew fight against Anti-pops' minions, aswell Streaming modem who wants to destroy th disc masters, but they are aided by HD DVD and Blu-ray, the baby ducks, Toothpick Sally, Recap, the real Chance Sureshot (it was a clone the one that died), the Guardians of eternal youth, Gary, Carter and Briggs, Death, Party horse and the Guardian of Lolliland (even she isn't supposed to participate), the baby ducks formed another mecha with Skips, Eileen, Benson (on top of the hat), the Guardians of eternal youth, Gary, Carter and Briggs, Death and Party horse, then they fight the modem, Anti-pops minions' shoot down Rigby's ship but is catched by Mordecai, and Chance shoot the Uber driver, the modem is beaten with Gary's synthesizer, a shockwave from Bluray and HD DVD and a, elbow drop from the guardian of Lolliland.
As they ended the first part of the battle, Anti-pops reached his ultimate power and started erasing Lolliland, Muscle man and HFG were caught in the erasing beam and Pops tried to save them but he was too scared of failing, so they said their last "my mom" joke before dying. With their death, Pops got angry enough to reach his ultimate power and the real cosmic battle started, both brothers fired their beams on Lolliland, but Pops was still scared of failing and Anti-pops was stronger so he erased everyone, including Andy, but Mordecai and Rigby.
With the death of almost all his friends, Pops engaged the fist crash that would reset the universe, Anti-pops would counter-attack it, as Mordecai and rigby were looking it, Mordecai thought of shooting Anti-pops before their fists collide, but their shots didn't affected him and they are caught in the middle of the punch
The Power: After the events of Part 2, The episode begins the same way as the first episode of the series, titled with the same name. After the "fight" with Beef Burrito, Rigby gets a sense of deja vu, and remembers all past events from the show, they go outside and dig up a futuristic Blu-ray box that holds all the memories from Regular Show, after being dead in the reality in which they fight Anti-Pops.
Mordecai remembers what happened, and they look around, they're in a glitch in which time didn't reset, and all other characters are just bland white outlines, caused by the "deletion" of them by Anti-Pops. They use their magical keyboard to go back to the End, and witness the fight of Pops versus Anti-Pops. "Guess who's not dead after all."-They shout at Anti-Pops. He attacks them, throwing them back on Lolliland, as it blows up, destroyed to pieces.
Pops is knocked back to a space in time and he finds himself in The Naive Man from Lolliland short. He escapes, and dodges giant letters that form Regular Show in the background (alluding to the opening title seen in every episode). He tries to save Rigby but is knocked back by a giant swarm of Adhesive Notes, as Mordecai's space is turned into a storyboard, and Rigby is made of the Adhesive Notes as well. "The fabric of reality is unraveling." -Anti-Pops laughs.
He sees Mordecai and Rigby threatened by Anti-Pops, and teleports to save them, putting them on a nearby asteroid. Anti-Pops taunts him- "Pops! Show yourself, coward!" "I am here" -he says. His twin brother gets ready to attack, but Pops launches himself, hugging him, purple energy covering both of them, and having Anti-Pops shrink down to his normal size.
Anti-Pops promises the minute Pops lets go he's going to "blast him into nothing". "I know, so I'm not going to let go." Pops sends himself and Anti-Pops straight into the Sun. As Mordecai and Rigby scream for Pops to return, he telepathically speaks to them. "Don't worry Mordecai and Rigby, I know you're sad, but I promise this is a happy ending. Take care of each other, goodbye."
"My God, all those one-star reviews, ah, I wish I could take it all back", Anti-Pops, now accepting his fate, says.
"You can try, you and I together, brother." Anti-Pops smiles, hugging back, as they are both obliterated by the star. Mordecai and Rigby are deeply saddened by the death of their good friend and, knowing this is it, want to come back as different animals when the universe resets. A giant super-nova forms, and Mordecai and Rigby are sent back to reality. Just like that, the universe is restored to its rightful balance, as news reporter Del Hanlon receives news that the Park Dome is finally back, after 3 years in space. Margaret, also reporting at the time, leaves her post and runs to see the group again after a long period of being apart.
Mordecai, Rigby and the others exit the dome to see hundreds of people. Their relatives run to hug him. Mordecai and Rigby's parents, Don, Muscle Man's wife Starla, and their newborn child. Skips reunites with Techmo, Margaret hugs Eileen, Hi Five Ghost hugs Celia, and Benson's pig comes to see him. Rigby suddenly kisses Eileen for the first time and both blush and smile after. They're all happy, but Ice King hears cries while giving an interview. It's Finn, grieving over the loss of his loved henchmen.
A statue of Gunther is built. Benson leaves flowers on the statue, while they all grieve in silence for the loss of Gunther. "He Broke the Bottles. He Loved to Making Mess. He Saved the Universe. He Was Our Friend. Gunther" is written on a plate on the statue.
Finn and Jake part ways after six years of working together in the park. They hug, and drive to their new homes, with Mordecai moving into his own place, and Jake and Princess Bubblegum moving into Princess Bubblegum's castle together, leaving the Park once and for all. Finn is working as an abstract comic creator, along with Susan Strong, showing paintings at an art gallery (some of which look like C.J. and Margaret). He meets Stef, a Bat-like girl whose collection is also on display. They both stare at each other. Jake, is seen teaching his child how to play games. Lady Rainicorn brings sandwiches for them, and they hug. Princess Bubblegum become a new generation of the queen of Ooo. Finn and Susan Strong are now reunited with new parents.
25 years later, all of them come to a reunion. Mr. Maellard had passed away, and a statue commemorating him has been built, right next to the statue of his very son he lost long ago. Everyone has numerous children, and they all gather for a picture. Finn and Jake sit down on the steps of the castle to talk again after all this time. Finn wished Marceline was alive to see what has happened the last 25 years, but Jake reminds him that they wouldn't have all of this if it wasn't for Marceline. Then, they leave to go play video games with BMO, but not before they shout their beloved catchphrases one last time ("Adventure Time!")
We slowly pan out of the house until we see a Hanatronic TV found somewhere in what appears to be Heaven itself, where a tape titled "Regular Show" ejects from a VHS player. Then, Ice King arguing with Gunther, knowing his dear friends are moving on with their lives now that the universe is saved. "Jolly Good Show" he says, relaxedly quoting his own well-known catchphrase, as the screen fades to black and the episode, as well as the series itself, officially concludes.