Adventure Time’s third season represented an evolutionary leap forward for the show, taking Pendleton Ward’s template – a preschool mix of Dadaism and Dungeons & Dragons portioned out in eleven minute episodes – and directing towards experimentation and serialisation alike. The third season featured a range of episodes that deviated from the established formula of “Jake and Finn go on an adventure and wacky shit happens” with a gender-switching episode, an episode entirely focused on periphery characters and an episode inspired by a David Lynch movie. It also began to flesh out the Adventure Time world’s hitherto undeveloped history, with a surprisingly touching backstory introduced over a two-part pair of episodes.

The show’s fourth season, now out on DVD and Blu-Ray in Australia, maintains this degree of originality, which is both fantastic and slightly disappointing. Disappointing not because of a substantial drop in quality or a trend towards conventionality – neither are in evidence, thankfully – but because the maturation evident moving from season two to three isn’t really on display here. If the third season pushed the show into third gear, then it seems its subsequent season is content to stay in that gear when I would’ve hoped for an upwards shift.

It’s a bit silly to complain about a show for not meeting my own personal expectations, though, and if season four set out to emulate season three’s successes then it has certainly done well. By only episode two we’re met with “Five Short Graybles” – probably the season highlight – which ties together five chapters, each spanning a couple minutes and each centring on a different one of the five senses. Only a couple episodes later, “Return to the Nightosphere” and “Daddy’s Little Monster” provide another two –part episode; this time with a dark tone to match the hellfire-and-brimstone aesthetic of the appropriately-named Nightosphere.

There’s no return of Fionna and Cake(more’s the pity), but we do get to see Princess Bubblegum and Lady Rainicorn save the day after Finn and Jake are captured in “Lady & Peebles” (which sees the legendary George Takei return to voice the sinister, seductive Ricardio). The Ice King’s backstory is expanded upon in “I Remember You,” which reveals an unexpected link with another core character, but this is again relegated to a single episode in a season that mostly consists of stand-alone episodes (outside of the cliffhanger finale).

Not that standalone episodes are a bad thing, mind. BMO, much like the Snow Golem in season three, gets an episode all to his/her own in “BMO Noire,” where a hunt for Finn’s missing sock reveals BMO’s sordid links with the treehouse’s animal inhabitants (if “Five Short Graybles” has any competition for best episode of the season, this is it). And one of the ongoing threads of the season – Finn’s burgeoning romance with Flame Princess – inspires a Hamlet homage in “Ignition Point.” “Hug Wolf,” meanwhile, is a surprisingly dark episode for a children’s program, using the werewolf trope to (arguably and indirectly) address sexual assault.

Not that darkness is entirely unexpected from Adventure Time. Despite its sunny, silly surface, the show has always had an undercurrent of sadness, an undercurrent reinforced by the affirmation that the show’s world is a post-apocalyptic one. That sadness is at its most pronounced in this season – particularly in the case of Marceline – and demonstrates that the show continues to mature even as it holds – perhaps too closely – to the template of the season prior.