For my good buddy Neverthrive's birthday a short time ago; posting her because Finnceline, man.

Disclaimer: I do not own Adventure Time and make no profit from this submission.

Blood hit the ground, as well as a significant amount of some… stuff, she wasn't exactly sure. It was shiny, like metal and crystal in the same thing, and its was not so much faceted as one big facet that the light around it turned into a burning blaze of light as it hit the ground.

Marceline picked it up, not so much dodging the blast of pure destructive forces that came her way as simply letting it pierce right through her shoulder. She barely blinked, the torn strands of her hair reforming like waves splashing over an empty place on the sea, and the hole in her body sealed up just as easily without the slightest bit of pain from her.

The giant foot, rather a paw all five-fingered talons longer than a house was taller and serrated at every angle so that it had to have a Nightosphere of a time just walking in a straight line, came down. She brushed it aside, again without effort, and above her the crystal that gleamed like metal shifted, and a spike elongated at her-

She didn't move, but she flew, like dancing on the music of the multiverse, and it struck dirt alone, and was trapped. And her axe was lighter than the air she moved in in her hands but heavy enough to sunder whatever she didn't want alive anymore, and it swung with a noise like silk splitting-

The cut spike didn't bleed, but it did ooze something like ichor. She never forgot that smell after Finn and her found a octopus-headed thing from the sea and hit it until it died. Ichor was a very distinctive smell.

Something came at her, smaller than her and stout for its height, and so fast like a bullet out of a canon, and blue, and she turned, one hand out, her claws thinning to mere nails.

The hand that met hers, it was not especially large for a boy's. But it was strong, the callouses like scars and then the actual scars,and she grabbed it, she pivoted on nothing but empty air and the spaces between worlds and the power crashing inside like music, and she swung.

Finn moved and he was a blur; a sword caught the light, razor steel gleaming like a bit of the sun frozen into solidness, and the beast roared (a noise like continents cracking, Marceline considered), and again came that paw, bigger than a hill, and Finn dropped next to her, and then they were running, running.

And laughing. Free as the wind and just as wild, the sound of it an echo of a song in her heart and shoot it was totally worth the long wait of all those years to find an echo of herself like him, heck yeah.

They danced. Apart and together, closer and then further, and where they moved the monster's paw did not hit them but the ground, churning up piles of dirt and pulverizing stone, and they weren't there to be hit, and its subsonic growls were getting louder the more they frustrated it.

"Now?" Finn said hopefully.

She grinned, her teeth like blades eager for blood. "Now!"

She grabbed Finn again, tossed him up; he went over the architectural curve of the beast's side, and it turned sideways to see him, and so it did not see her growing, her body swelling as her magic became biomass and her body growing beyond control; one moment she was a human-sized woman, and the next, she was just as big as this monster (perhaps a touch smaller, more or less), scales and flying tentacles and a yawning maw filled with hellflames that glowed brighter as she roared.

She grew with impossible speed, so that her sudden mass made a shockwave burst tearing up the great, and the beast above her was shot into the air. And Finn was still on it, ramming his sword into a vulnerable spot where neck met back, so that it twisted and flailed as Marceline's many tentacles curled up and rocketed into its belly like a thousand punches-

Her mouth opened as Finn drove his sword in deep. Flames coupled with a sword, and the former went through the beast as the latter pierced a relay organ.

It's fall was like a mountain coming down. Marceline dived out of the way, grew wings, and she flew up. A tentacle the size of a small building caught Finn, and smooth-lipped suckers bigger than he was held him tight like intense hugs.

The beast hit the ground. IT was already dead.

And Marceline fluttered to the ground, her wings receding. A smaller tentacle flipped up, smacked Finn on the bottom with a sucking pop ("Eep!" Finn squeaked, rocking a bit as her massive proportions shook with inhuman chuckling), and then there was a flurry of biological motion.

Finn dropped down. Marceline rose up to her normal height and form again (a stray tentacle coming apart and becoming hair) and she brushed herself down. "Dude, dude, that was awesome!"

"Aw, yeah!" Finn said, and they high-fived.

"…So, we gonna take the head or something for a trophy?"

Finn looked at the beast. Its head alone was bigger than a house.

"Maybe just a tooth," Marceline amended.

—-

"Looks great," Marceline said a few hours later, back into her home (now feeling more like a home than ever, Finn's smell and Finn's warmth in it like a fire), as Finn jammed the fang into place into a random wall.

Finn nodded, as Ice King wandered in the background (because he lived there apparently). He blanched at the looks they were giving each other and hurried away into some other dominion. He ran into Princess Bubblegum on the way, who was there installing secret cameras so she could spy on the love-times 24/7 to entertain her secret kinks (and she was crazy nosy). Ice King hugged, for he considered such depraved, and shooed her away despite her protests.

Finn coughed. "Um…"

Marceline put her arm around his head, pulled him close and gave him noogies before she kissed him on the cheek. "S'up?"

He giggled and squirmed, trying uselessly to escape her monstrous strength, and he said, "You're a dork!"

"Nuh uh, you're a dork!"

"You're a mega moofus dork!"

"The plop is a moofus?"

"It's like a dork or a… uh, mophead?"

"You made that up because you liked how it sounded."

"…Got your nose!" And Finn leaned up on his tippy-toes, and with Marceline leaning down and hunched over, he could stand tall enough to kiss her on the nose, his lips brushing soft and sincerely against the broad tip. "Mwah!"

Red bloomed on her face. She snorted and patted him on the back hard enough to knock him down and she said, "That doesn't count!"

"Does to," he said smugly.

Marceline chuckled and jumped on the couch. It was a newer, much softer one. Finn did the same, flopping down with her, and she said, "You know, for a total dork, you really liven the place up." He grinned and kissed her again. "But no telling anyone I go nuts for kisses or I'm punting you off a thing. I got an image to maintain!"

—-

"Aww, so sweet!" Bubblegum said, wiping away a tear.

"Uh, I'm getting really uncomfortable," Ice King said. "Are you getting uncomfortable? I know I am."

"Hush! Now they're kissing! And… oooh! Oooh! Aw yeeah, that's what I'm talking about!"

"What are you- OH DEAR GLOB SHIELD MY EYES!" He covered his face. "That's just wrong!"

"I didn't even know you could use tentacles like that," Bubblegum mused.

"Stop talking, please!"

"Though I suppose since they are slimy, they're naturally lubricated so-"

"DEAR GLOB, STOP!"

"Hey, you stop ruining my jollies, my brain-meats are a-working!" She bonked him on the head. "Ooh, nice, that one's going into my personal collection! Uh huh!"