The series at large follows the adventures of Finn (a human boy) and his best friend and adoptive brother Jake, a dog with magical powers to change shape and size at will.

Finn and Jake live in the post-apocalyptic Land of Ooo, where they interact with the series' other main characters, including Princess Bubblegum, Marceline the Vampire Queen, and BMO.

[8][9][10] Several of the show's crew members were then hired for Cartoon Network's Summer Camp Island, created by Adventure Time storyline writer Julia Pott.

[17] Many of the cast from the original series returned for the specials, including Jeremy Shada as Finn the Human,[18] John DiMaggio as Jake the Dog, Niki Yang as BMO, Hynden Walch as Princess Bubblegum, Olivia Olson as Marceline the Vampire Queen, and Steve Little as Peppermint Butler.

[21][22] Guest voices include returning cast members Maria Bamford, Ashly Burch, and Ron Perlman, as well as Randall Park, Stephen Root, John Hodgman, David Bradley, Chris Fleming, Isabelle Fuhrman, Andy Daly, Ron Lynch, Tom Scharpling, Bill Hader, Julia Butters, Patti Harrison, Toks Olagundoye, Edi Patterson, Bex Taylor-Klaus, Dana Snyder, Duncan Trussell, SungWon Cho, and Anthony Head.

[23] Longtime Adventure Time executive producer Adam Muto returned to oversee the production of the specials, with Jack Pendarvis, Anthony Burch, Jesse Moynihan, Christina Catucci, Charley Feldman, and Kate Tsang serving as part of the writing staff.

[24][25][26] Storyboard artists who worked on these specials include (but are not limited to): Ashlyn Anstee,[27] Jim Campbell, Iggy Craig,[28] Megan Fisher,[29] Laura Knetzger, Hanna K. Nyström,[30] Maya Petersen,[31] Anna Syvertsson, Mickey Quinn, and Serena Wu.

[36][37] The end credits of the final special "Together Again"[23] feature a dedication to four deceased members of the show's cast and crew: Polly Lou Livingston,[38][39] Miguel Ferrer,[40][41] Michel Lyman,[42] and Maureen Mlynarczyk.

[60] Alexander Sowa of CBR argued that Hugo is a futurist akin to Elon Musk or Steve Jobs, whose characterization is "a clear satire of modern-day corporations and capitalists.

Joe Matar of Den of Geek noted similar themes, saying that the story is about those living in Drift realizing that "their Elon Musk-esque tech capitalist overlord [Hugo] is destroying their world," which forces them to come together and rely on one another.

[62] Robert Lloyd of the Los Angeles Times likewise noted that the special hints at social commentary toward the end, referring to the destruction of Earth, the nature of resource management, the importance of cooperation, and "the way that certain human billionaires look at space as an escape pod.

She wrote that the episode gives fans the "emotional payoff and answers" they have been yearning for and that the special uses the plot to explore Marceline's childhood trauma, her romantic history with Bubblegum, how the two are interconnected, and fills in gaps about her past.

Long also stated that while the special is not "as offbeat" as BMO, it is heavier in terms of emotional weight and plot, and making clear that "romantic subtext" in the original show has "always been straight-up text."

"[68] Petrana Radulovic of Polygon argued that 2020, when it came to all-ages animation, was a "glorious gay celebration that was unheard of just five years ago," the development of Marceline and Bubblegum's relationship in the "Obsidian" episode.

[48] At the same time, Princess Weekes of The Mary Sue, before the episode aired, said she found it reassuring because for queer representation "it is important to acknowledge that loving someone doesn't fix emotional issues or personality flaws.

Eric Kohn of IndieWire argued that the episode is "endearing, nice-to-have fan service" that isn't as ingenious as the show, but there is plenty to enjoy, with the reappearance various characters, and said it has a touching moment that resembles Pixar's movie, Soul.

"[76] Radulovic said that other than the character reappearances, the special is visually gorgeous," and serves almost a metaphor for the journey that Finn and Jake undertake in the show itself, calling the episode a "beautiful, powerful, poignant ending" which captures the emotional depth of Adventure Time itself.

[77] Alejandra Bodden of Bleeding Cool was surprised by the number of deaths in the episode; she wrote that while she enjoyed Peps, she found the special's plot to be "kind of a fucked up story and situation to be in."