- Anti-Climax Boss: After all the buildup throhought the series, GOLB is quickly defeated by Betty after she uses the crown to fuse herself with him.
- Author's Saving Throw: During an interview with TVGuide, Adam Muto revealed that those who didn't get focus (such as FP and HW) or had little focus in the finale already got closure along with their respective plot points (such as Finn's relationship with HW, FP and her issues with her father, Jake and his alien lineage, Marcy and her father) in previous episodes so that the finale wouldn't be cramped.Adam Muto: A lot of the episodes leading up to [the finale], we were trying to use to serve as the last episode for that particular character so we wouldn't have to cram too much in at the very end here. So there are scenes, but we already had our last major Lumpy Space Princess episode by the time we get to the end, and our last Flame Princess episode, so it was actually less dense by the end than it might seem. It was just sort of hitting the big [beats] and then finding vignettes for all the characters that we knew we wouldn't be able to give full stories to just so we could get snapshots of where they could end up.
- Broken Base:
- The Lich's absence from the finale. While some agree that he and his motivations were getting old, others wanted him to return in the finale with a final confrontation between him and Finn, especially with GOLB being involved with the plot.
- Finn's unresolved relationship with Huntress Wizard is either a sign that he's still too young for a serious relationship or a huge cop-out to fans after years of failed relationships who wanted to see a well deserved closure to his love life, especially with most characters in the finale having some scenes with a romantic moment.
- Critical Dissonance: The finale was highly praised by critics, but it got a mixed reception by the public and fans of the show. Even Adam Muto himself expected this to happen.Adam Muto: Half the people will definitely hate it, because that's every show's ending, but just having that experience instead of waiting forever.
- Epileptic Trees: It has been proven by the show itself that BMO is an Unreliable Narrator, as shown in "Ketchup". No one knows if most of the finale, which was told by BMO during the entire thing, was real or not.
- Fanfic Fuel:
- Many who didn't like how the resolution between Simon and Betty ended decided to give the couple a happy ending through their own means, whether by Simon managing to turn Betty into normal again or... Simon marrying GOLBetty.
- Since Huntress Wizard was Demoted to Extra in the finale and the ending montage didn't have a scene with her and Finn together, which ended leaving their relationship ambiguous after two episodes in the final season confirming their feelings for each other, many Finntress shippers decided to create their own resolution through fancomics, fanarts and fanfics, with both of them living together after the finale.
- Alternatively, Flinn/Smokybear shippers decided to do the same thing, but with Finn and Flame Princess instead, with both of them getting together again after the end of the series.
- Thanks to the kiss between Lemongrab and LSP, many fanartists decided to post and draw of fanarts of them both living happily as a couple.
- "Holy Shit!" Quotient: Princess Bubblegum and Marceline kissing. On the lips. Onscreen and uncut. In spite of what Olivia Olson said in 2014.
- Internet Backdraft: Fans outside of the US were not happy when they found out that Cartoon Network censored the finale in certain countries. Latin America had most violent scenes removed while Russia and Bulgaria had the kiss between Marceline and Bubblegum completely removed. Koreans got it worse, with most of the kissing scenes being removed entirely.
- Memetic Mutation:
- Misaimed Fandom: LSP and Lemongrab's kiss was received by some fans as a legitimately cute shipping moment instead of the joke it was almost certainly meant to be.
- Moment of Awesome: Bubbline becoming endgame despite CN initially not wanting it to be explicitly shown or confirmed earlier on in the show's run. Adam Muto credits Rebecca Sugar's Steven Universe in helping making this possible.
- Replacement Scrappy: GOLB. Many expected the being behind the Lich to be a force to be reckoned with. Once he finally shows up, all he does is... nothing. He only turns some of the Gumbaldians into an abomination, floats at the same spot and that's it.
- Tainted by the Preview: The airdate. When the first teaser was revealed, it only mentioned that it will premiere soon. The date the teaser was posted? March 19. Almost six months before the premiere. The fandom was not happy about this, especially during the period between the teaser and the reveal of the airdate.
- They Wasted a Perfectly Good Character:
Adam Muto: Beyond that, there were so many where its not necessarily important where do Finn and Jake end up? What happens to them? How old do they get? Who do they marry? Its important to focus on this section. This was Finns childhood and on the cusp of becoming a good adult. Hopefully hes a learned a lot and become a more complete person. He doesnt even have a sword through most of the finale at all. The idea of him putting down a weapon as the way to resolve a larger conflict ... this wont help in the situation. I think that was an important thing, not trying to show that.
- The Candy Kingdom Haters were expected by some fans to have a big battle against Princess Bubblegum's personal army, but they were barely in the episode and all of them run away after GOLB appears.
- Many of Princess Bubblegum's allies such as Huntress Wizard, Flame Princess, Cinnamon Bun, Slime Princess and Lady Rainicorn don't have a major focus at all in the finale, despite all of them being heavily advertised in the promos and official artwork.
- In a sense, Finn himself, despite being the main character of the show, comes off more as a secondary character here, not taking part on the final battle, not having most of his character arcs closed and having less presence during the ending montage. It doesn't help that Muto did not want to give him closure or take part in the final battle, according to an interview with Polygon.
- Many were also disappointed that The Lich didn't have a major role and was only given a single cameo.
- They Wasted a Perfectly Good Plot:
- There's a subset of fans who are upset about Finn being reduced to a Distressed Dude in the fight with GOLB. The poor kid didn't even get to do anything heroic against the Final Boss of his own show.
- Many fans were especially disappointed that Finn's love life didn't get any closure, or even a single mention, during the finale. Needless to say, fans are hoping that it gets addressed in the comics, as many wanted either resolution for Finn and Huntress Wizard's relationship, or for Finn and Flame Princess to get back together.
- Unexpected Character:
- Many fans were pleasantly surprised when a clip revealed that Maja would return for the finale.
- Additionally, few were expecting to see the return of The Duke of Nuts, Donny and The Jiggler, who haven't appeared since all the way back in the first season.
YMMV / Adventure Time S9E13 "Come Along With Me" ("The Ultimate Adventure")