Okay, saying this beforehand, this might turn out bad. Likely that would be because Adventure Time is cheerful and most of the fan fiction I write are sad. The one I was working on before this I had already thought out the ending. If I finish it, some of the other fans of that show will be angry. It's a really heavy ending. I'll try to not kill anyone or anything like that in this one.
Once upon a time, long after the Mushroom War, there lived two righteous best friends, Finn the Human and Jake the Dog. These two best friends dedicated their lives to saving those in trouble. More often than not, their adventures were halted by a wizard who was always kidnapping princesses, and that wizard's name was the Ice King. Ice King was not as evil as annoying, doing things such as trying to make friends with Finn and Jake and writing fan fictions about them. In the fan fictions, Finn was a girl named Fionna and Jake was a female cat known as Cake. Fionna and Cake were much like Finn and Jake, but their enemy was the vicious Ice Queen, who stopped at nothing when capturing princes. Fionna and Cake knew nothing of Finn and Jake and their adventures. They knew of their creator, and were quite fond of him. They knew of one thing, but not everything else. As fate would have it, things wouldn't stay that way for very long.
"Hey buddy, is something wrong? You look pale." Jake noticed this about his companion, Finn.
"Oh, nothing. Nothing's wrong." Finn replied.
"You've been looking like that since Ice King froze us and brought us to his castle." Jake stated. "Did something happen?"
"Nothing happened!" Finn exclaimed. Darn it, I'm letting Ice King's weirdness get me. Finn thought to himself. His gaze wandered to the window of the tree house just as the phone began to ring. Jake answered it.
"Hello?" Jake said to the person on the other side. "Yeah. Uh-hmm. Okay, we'll be right there."
"Who was that on the phone?" Finn asked his best friend.
"Oh, just Princess Bubblegum. She says something crazy-weird is going on in the Ice Kingdom, and she wants us to check it out for her."
"Ah, do we have to?" Finn groaned, laying on his back on the couch.
"Yes we have to!" Jake exclaimed, causing Finn to roll off the couch unconsciously with a loud thunk. "Unless you want to disappoint Princess Bubblegum. And I know you don't want to do that, do you?"
"No, no I don't." Finn sighed.
"I'm serious man, nothing-" Finn said, only to be shushed by Jake, who began to sniff the air. "What up?"
"Do you smell that?" Jake asked.
"Um, I'm not a dog, Jake."
"It smells... like, like..." Jake began.
"Like what?" Finn exclaimed.
"Like that!" Jake pointed at a huge vortex next to the Ice Castle.
"Flip!" Finn shouted. "What the zip?"
"Ah, Finn, Jake!" the Ice King flew down from his castle to the two best friends.
"What did you do now, Ice King?" Finn asked.
"What? I am shocked that you would so easily come to that conclusion, I-" Ice King began.
"What did you do!" Finn screamed.
"Fine, come with me, I'll tell you." Ice King explained. He began to lead Finn and Jake up the path to his castle. "It all began when I found one of the magic tomes from before the Mushroom War. Not something too odd, but this one was different from the others. It was pop-culture magic."
"What the heck is a pop-culture?" Jake asked.
"How the heck should I know?" Ice King answered. "All I know is there was a spell to bring fan fiction characters to life."
"You didn't!" Finn said.
"Didn't what?" Jake asked.
"Oh, I did. I got everything for the spell and did everything the spell said to do, and it worked. I brought Fionna and Cake from their Ooo to our Ooo." Ice King grinned, then frowned. "But something went wrong."
"Like that hole floating in front of your window?" Finn said.
"Who the heck are Fionna and Cake?" Jake exclaimed. "Finn, do you know what he's talking about?"
"They're part of a fan fiction I wrote." Ice King said. "And yes, the vortex happens to be part of what's wrong. But the major thing wrong is, they hate me!"
"Come on Fionna, why won't you talk to me?" Ice King asked the girl, whom he had locked in the cell he had in his castle. She simply hmphed at that. "Cake, what about you?" The cat also turned away from him and hmphed. "Why don't you love me?"
"They probably hate you because you locked them in a cage." Jake pointed out.
"Where are they now, anyway?" Finn asked, his back turned to the cage.
"Um, still in the cage." Ice King said. Finn looked around. "Behind you." When the boy finally figured out where the cage was, Fionna had her face pressed to the bars, scowling.
"Oh, hey there, fellow human." Finn smiled, walking up to the bars.
"Why are you talking to that loser?" Fionna asked Finn.
"Why don't you love me?" Ice King asked the girl. "You loved me in the fan fiction!" He held up the fan fiction, and Fionna slapped it out of Ice King's hand.
"That's because I didn't know you were a big nerd in real life." Fionna said.
"Yeah!" Finn agreed.
"Silence you!" Ice King screamed at Finn. He then noticed Jake using his key hand to open the cell. "You! Stop that!" Just as he was about to freeze Jake, Finn kicked Ice King in the head.
"Here's a tip on how to make friends: don't lock them in cells, don't try to feed them your feet in omelets, and don't freeze them!" Finn exclaimed. Jake had the cell unlocked and scooped up Finn, Fionna and Cake, stretching out the window and shrinking back outside.
"Ah, darn it." Ice King said, laying on the floor of his castle. A penguin waddled up to him. "Gunter, why didn't you stop them?" The penguin simply quacked.