Fionna and Cake feels like a fever dream for Adventure Time lovers. The new spinoff picks up years after Adventure Time's finale, roundabouts the timing of the spinoff movie Adventure Time: Distant Lands: Obsidian. But its eponymous characters began as in-show fan-fiction concocted by the kooky Ice King, in a playful diversion that gender-bent all of the characters of Ooo for fresh fun. So how did Adventure Time showrunner Adam Muto spin these two into a whole new mini-series when Fionna and Cake weren't even canon?

Honestly, the answer is a mindfuck. But we should expect nothing less of this cuddly cartoon series that was slyly set in a post-apocalyptic Earth, where nuclear war gave way to goo-filled zombies, cackling vampires, powerful princesses, scads of magic, and hordes of critters made of candy.

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How Fionna and Cake fits into — or is retconned into — Adventure Time is far from the most compelling thing about it. Incredibly, Muto and his team do more than resurrect beloved characters and familiar voices. They use each episode to plunk audiences into a different realm of the multiverse. While that's a concept that's arguably been done to death in movies, here it offers audiences curious new incarnations of characters like Princess Bubblegum, Marceline the Vampire Queen, the Ice King, and many, many more. Some will be winsome, magical, or even musical. And some will make your head spin and your heart hurt. You've been warned.

What's Fionna and Cake about?

Fionna and Cake are not loving this world. Credit: Warner Bros. Discovery

In Adventure Time, Fionna the Human and Cake the Cat were very directly Finn the Human and Jake the Dog with a gender swap — one that touched every resident of Ooo, resulting in Prince Gumball and Marshall Lee the Vampire King. But in the opening episode of Fionna and Cake, there's no magic or sword-swinging adventures for the titular twosome. Instead, they live in "crummy apartment...in a sad little city," where Fionna has a shitty job, Cake can't talk (much less shapeshift), and PB's counterpart is Gary Prince, an aspiring baker who dreams of crafting yummy figures out of food. Marshall Lee's vampire bite is a mole on his neck, and even LSP makes an appearance far removed from her spacy origins. The closest thing to a quest in the premiere is Fionna trying to take Cake to the vet. So what's the deal?

The first two episodes that premiere on Aug. 31 won't answer that. Instead, they'll introduce you to Fionna and Cake's ennui then pivot back to Ooo, decades after the Adventure Time finale. There, Simon Petrikov (formerly known as the Ice King) is miserable, pining for his lost love Betty — and even longing for the oblivion the madness of his old crown offered. He's still got friends in Marceline — though she's caught up in love with Bubblegum — and Finn, who is beefy, bearded, and adventuring with the late Jake's son T.V. But there's an emptiness that they cannot fill. As Simon searches for meaning he discovers the stories he wrote "in a fugue state" may be what saves him — or destroys him.

Fionna and Cake is more than adventure time — it's a tale of regret.

Simon can't let go of the past in "Fionna and Cake." Credit: Warner Bros. Discovery

For those of us who went on the rollercoaster ride of loathing the Ice King for his sexist princess-harassing to loving him as the broken romantic/adoptive dad who saw little Marceline through the Mushroom War fallout, seeing Simon cured but unhappy is pretty wrenching. He's woken up in a world where he doesn't fit in, and where all he possesses is pain and regret. Even when others praise his Fionna and Cake stories, he can't connect to the version of himself that wrote them. Perhaps there's a reflection there for the creators of Adventure Time who look back and can't relate to the versions of themselves that started with a candy slumber party invaded by zombies. Perhaps Simon just speaks for any of us who hit middle age and fear our best adventures are behind us.

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Then, with each episode — airing in pairs until the finale on Sept. 28. — Fionna and Cake turns the knife. Not unlike Everything Everywhere All At Once (or even The Flash), Simon gets an insight into the multiverse, seeing how his story and those of his loved ones might have played out differently. He's tormented by the possibility that he could have done better with the crown, haunted by how he might have failed his adopted daughter, and compelled to help his friends no matter what incarnation of them he stumbles across — including Fionna and Cake.

It's enthralling to be thrown into these different worlds, some familiar, some wholly new and nightmarish. Adventure Time has always been surreal. But here, it shed the vestiges of children's programming, wallowing in deeper emotional depths and even cursing. ("Oh my glob" has been swapped for "Goddammit!") In the eight episodes (of 10 being released) that were allotted to critics, there were plenty of moments where this long-time Adventure Time fan was giddy over a new interpretation or a quirky callback, like Fire Princess as a hunky DJ or the Cheers theme playing casually like it won't give us trauma jitters. But like Adventure Time: Distant Lands: Together Again, which grappled with Finn mourning the death of Jake, Fionna and Cake confronts grief. A grown Finn — who as we saw in Obsidian has a Jake tribute tat — consoles Simon, but can't really comfort him. They're at different stages of their journeys, Finn having reached acceptance; Simon digging his heels into denial. And as Simon rages against his heartache, he is reminded in a twisted It's A Wonderful Life way how he is better off and worse off. And how that's just life.

Fionna and Cake is a resplendent story of love.

That's Finn! Credit: Warner Bros. Discovery

Without giving too many of its surprises away, Fionna and Cake isn't all Simon sadness. As she did in her Adventure Time eps, Fionna fumbles into flirtations, funny and disastrous. PB and Marci find each other in different forms, including one that will surely have their shippers freshly exultant. But as it ever was, this Adventure Time spinoff is ultimately a celebration of the families we build ourselves.

In a world of monsters, madness, and a candy fascist, little lost baby Finn found Jake and his parents. Cursed Simon found little vampire kid Marceline. Bubblegum made her family and minions from her own sugar and spice and science. As the series went on, more and more oddball but devoted families emerged across the kingdoms. In Fionna and Cake they stretch across the multiverse. I wish I could tell you these found families will get through their harrowing showdowns to a happy ending. I wish I knew. But I haven't seen the two final episodes, and the cliffhanger critics have been left with is a dizzying one-two punch of horror and hope.

But I can safely say, if you loved Adventure Time you will treasure Fionna and Cake. Just brace yourself, because this cartoon spinoff goes hard on your feelings.

Fionna and Cake episodes 1 and 2 debut on Max Aug. 31, with two new episodes airing weekly through sept 28.