The episode begins with Finn and Jake emerging from tall grass to begin their Safety Patrol. Jake is dressed to the nines in his uniform, but disappointingly, Finn isn’t wearing his. The two observe a possibly sinister-ordinary, little town full of House People. The ordinary calm is quickly shattered with the introduction of our titular character, Donny. 

Donny is a large, green grass ogre with a large mouth and eyes. He has red cheeks and a leaf over his groin, to preserve his modesty. Donny is harassing the House People and their chickens and is quickly placed under arrest and sentenced to his tiny jail cell. Being the jerk that he is, Donny flips Mr. Jail on his back and laughs as he struggled like a turtle.

Finn and Jake call out Donny and it’s clear that Donny’s talents lie with his strength and not his wit. Finn and Donny begin to grapple with Finn’s skill quickly earning him the advantage. Donny tires after Finn puts him in a headlock and the two pause their fight. Finn easily compliments Donny only for the grass ogre to respond with insults and hurt Finn’s feelings.

Best big brother, Jake, defends Finn’s honor by threatening to gore Donny with his 21-point antlers. Donny is quick to pass the blame to Finn and Jake for taking the situation too far when all he was doing was messing around. Jake proclaims that Donny is one messed up dude after watching him storm off. Finn defends Donny, stating “Nah, he’s just rough-and-tumble like me. But deep down he’s probably really sensitive like me.”

Finn invites Donny to hangout at their tree fort for video games and apple juice. Jake asks for Donny to wear pants, a seemingly hypocritical remark until Jake reveals that he is wearing pants of pixie-woven spider webs. After losing to BMO’s Bug Battle game, Donny throws a spectacularly jerky tantrum but genuinely seems unaware how he’s being a jerk. 

Adventure Time becomes Moral Time.

Before Donny can truly grasp the concept of empathy, Finn hears a cry for help and leaves Jake to continue Donny’s lessons.

Finn returns to the House People village to find werewolves attacking the citizens. Even Mr. Bank gets his back end broken off, but rest easy because his assets are insured. Through skillful maneuvering, Finn traps both wolves in Old Mister Well. Finn looks at the destruction done to the village and asks the all important question…

WHY?

Why indeed.

The wolves down in the well reveal that they are not Werewolves, but Why-wolves, creatures  possessed by the spirit of inquiry and blood-lust. The Why-wolf lectures on how Finn disrupted the balance of the ecosystem by removing Donny. The Why-wolves were now free to terrorize the House People by losing their only deterrent, Donny’s pungent gas, obnoxygen. Without Donny and his obnoxygen, the Why-wolves population will grow out of control until they are all eaten by the Cosmic Owl. 

Realizing Donny’s importance, Finn returns home to find that Jake did too good of a job of teaching Donny. Donny now plays the cello and speaks with better manners than Jake has ever exhibited. Even his appearance changed with Donny sporting a grass hair curl and wearing jeans with shoes. Donny shows off his new array of helpful songs like, “Eight ounces, Eight glasses, Eight days a week” and “Got to get pants, Go get your pants, Button, Fly!”

Finn explains that Donny needs to be a jerk again in order to save the House People but Donny clearly states his intentions of never being a jerk again. He is turning over a new leaf (guess where he pulled it from) and that Finn will respect him when he says no.

Moral Time becomes Trolley Problem Time!

What’s the greater good? Letting Donny live his life happily as a nice grass ogre but everyone will likely die horrible deaths to the Why-wolves until the Cosmic Owl comes or forcing Donny to become a big enough jerk to produce enough Obnoxygen to subdue the Why-wolves and keep the House People and everyone else alive.

Well, Finn’s a hero right? He’ll always protect the little guy. 

So, Finn and Jake drag Donny, kicking and screaming, back to the village where the House People are getting ravaged by the Why-wolves. Donny thinks that he can persuade the wolves to stop with his musical lessons (unfortunately we do not get to hear about the ethics of laundry or crosswalkery) but his hair ditty doesn’t catch the wolves attention. 

By not being a jerk, you’re being a real jerk, Donny

Finn realizes that Donny is sensitive about his songs and proceeds to make fun of his songs. Jake catches on and soon both the Why-wolves and House People are laughing at Donny. Enraged, Donny bursts out of his clothes and changes back into a full-blown jerk. His clouds of Obnoxygen cause the wolves to retreat, saving the House People. Finn and Jake congratulate Donny  but he rebuffs them “Housies, ready to hear my new song? It’s about how Finn will betray you just to save lives.”

Finn apologizes to Donny, wearing the weight of his decision on his face. Best big brother, Jake takes Finn to go stare wistfully at the lake. Donny revels in the return of his jerkiness, though he looks like he’s forcing himself to enjoy it. Donny stops his tirade on the House People to watch Finn retreat, whispering that he would never forget him.

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Marceline is an “evil”, supernatural, thousand-year-old vampire queen, but more importantly she is cooler than you.  She is always out late, can sing and play an instrument, changes her outfit/hair between episodes, probably really loves Halloween, owns a lot of cool spaces around town and can be really intimidating when she needs to. When we open the episode Finn and Jake are doing dumb baby things like playing in what appears to be a dragon graveyard.  Marceline is creeping from the bushes and finds an opportunity to mess with their innocent heads.  Kind of weird to start with Marcy there actually, and it wasn’t in the storyboard—but I assume it was added in so that we, the viewer, know that Marceline is only posing at being evil allowing us to enjoy her antics instead of actively rooting against her “evil deeds”.

Finn and Jake have only met Marceline once before when they were evicted from their home.  It was a fun introduction, but in this episode, we actually get to see more of her personality and interactions.  Turns out she’s very much a teenager.  Well, not really. Marceline is at least a thousand years old—that’s older than wrinkly old Yoda from Star Wars.  But Marceline retains a more youthful, cooler, energy of a mischievous baby Yoda.

Marceline is just a new type of individual to a person like Finn.  Outwardly and on first impression it seems like she might be mean and is kind of scary.  Or is she messing with him?  Why is she into summoning the undead?  She makes me ask so many questions!  But also she makes everything really fun! For the rest of the episode they perform evil deeds only for Marceline to reveal she’s messing with Finn’s innocent head. We even get a return to the Duchy of Nuts where calls for the duke’s execution (as suggested by his wife, the duchess) have seemingly passed! The writers really get their nuts-worth this season as we never ever return to here or any of their characters for the rest of the series.

Jake gets a sub-plot where he’s trying to “save” Finn from his newly-found status as Marceline’s henchman.  A lot of Jake’s conflict in doing so is his fear of vampires as previously established in Evicted!  But you can also read this as Jake representing Finn’s youth whereas Marceline represents Finn entering a more complex stage of his life in becoming a teenager.  Jake wants to “save his bro from a scum-sucking vampire”, but also maybe wants to spare him from the nuances of teenage emotion and instead partake in going down slides on a dragon playground instead.

Meanwhile, Marcy has no qualms spooking Jake whenever she can and outright mocks Finn’s lawful good nature.  She’s never really serious and it would appear that she’s just being mean to Finn—but this is just how some people (or thousand-year-old supernatural beings) act when they interact with people.  It’s not until later in the episode that we hear her open up to Finn and say something meaningful.  When prompted by Finn why she is out in the sunlight:

“Yeah, it hurts.  But I kind of like it. Reminds me of when I’d scrape my knee up as a kid and my mom would patch me up.  You know what I’m saying?””

Clearly she doesn’t hate Finn and feels somewhat comfortable enough with him to share that.  At this point Finn sort of realizes the kind of person Marceline is and his fear of hurting someone is lifted.  They became friends despite Jake’s best efforts. 

But wait, Jake finally gets over his fear of vampires (or is it fear of his friend growing up?)!  He wears his best disguise, which when compared to previous attempts, is a unique success in that he actually managed to stay hidden and vanquish his foe with a surprise attack!  It was all make-believe though.  Marceline is left unharmed and Jake is free to run through the strawberry fields with eternal youth in his heart.