Author's Note: Each of my stories is a continuation of the previous story. In order to understand this story, it would be excruciatingly helpful to read my other three stories first. However, if you're too lazy to do so, here's a brief summary of what's happened in my little Adventure Time universe.

Princess Bubblegum and Marceline became better friends.

Ann and Marie, a troublemaking duo of thieves, were introduced.

Finn was turned into an adult by a magic spell.

Finn went to a bar and ended up in bed with Marceline.

The magic spell wore off, and Finn was turned back to his normal age.

Marceline got pregnant and gave birth to Finn's new son, Benjamin.

Marceline promised to turn Finn into a vampire on his eighteenth birthday.

But seriously guys, give my first two stories some love. They would be really helpful in context to this story.

Benjamin was inspired by ilikekorn, and Violet, Fionna and Marshall Lee's daughter was inspired by an anonymous reviewer on my previous story, Baby Blue Bat, called Marshall Lee Luv.

Our story begins on Finn's eighteenth birthday. Benjamin is supposed to be about five years old. Let's just assume that vampires age normally for their first few years. Enjoy.

Disclaimer: I do not own Adventure Time with Finn and Jake. It is owned by Pendleton Ward. I also do not own Mortal Kombat.

"How's this, mom?"

"Move it a little higher, Benny."

The young vampire floated closer to the ceiling, a bright blue streamer in hand, and held it up against the wall. "Is this any better?"

Marceline stood beneath him, studying the arrangement of the decorations. "Yeah, that's good."

Benjamin taped the streamer to the wall and went to his mother's side. He mimicked her posture, placing one hand on his chin and the other on his hip, pretending to contemplate the room's decor. Marceline noticed his imitation and smiled, putting an arm around him. He looked up and smiled back. "I can't wait for the party, mom. It's going to be huge! Do you think daddy will like it?"

"I'm sure he'll love it."

There was a knock at the door. Marceline flew to the door with Benjamin close behind. She opened the door to find Jake, Lady Rainicorn, and a few other guests.

"Hey Marcy," Jake said. He held up a large, clear cake box full of Finn cakes. "Where can I put these?"

She pointed toward the kitchen. He started walking in the indicated direction, and she followed him.

Benjamin grinned up at Lady Rainicorn. "Hey, Aunty Rainicorn, where is everyone?"

Lady smiled back and floated inside. Trailing behind her was a quintet of rainicorn pups, five creatures with the face of a dog and a rainbow for a body. Four of them barked and swarmed Benjamin, jumping up on him and licking his face. He laughed and tried to wrestle the pups off him.

When they had finished greeting Benjamin, the pups began to wander aimlessly around the room, sniffing things and zapping random objects into different colors with their tiny horns. One pup stayed with Benjamin.

He held out a fist to the dog. "Hey man, do you want to play Mortal Kombat?"

The pup bumped his fist with a paw. "You know it!"

They floated up the ladder to his room, which was divided from Marceline's room by a wall constructed by Finn and Jake themselves. Schwabl the zombie poodle growled when he saw the rainicorn pup Jaime and dived under the bed. The two cousins laughed.

As he fired up the Play Station, Benjamin couldn't help thinking how lucky he was to have his cousin around. Jaime was the only rainicorn pup who inherited Uncle Jake's magical genes, so he was the only one that acted more like a person than a dog. Benjamin felt like he could never ask for a better best friend.

"I'm so going to beat you this time!"

"Dream on, Benny!"

Meanwhile, downstairs, more guests continued to arrive, including Ice King (They never exactly invited him, but they figured that he'd be less destructive if they just let him stay), Lumpy Space Princess, and various other candy people. Jake helped Marceline continue to set up for the party. They were currently sitting on the floor, blowing up balloons. Between gulps of air, Marceline asked, "Jake, are you sure that you're o.k. with this?"

Jake nodded. "If it'll make him happy, I'll be fine." He stopped suddenly and sniffed the air. The rainicorn pups flew to the windows and began barking excitedly.

Marceline swept the empty balloons under the couch. "They're here! Everyone hide."

Jake stretched out his arms and tried to round up his children, but they kept squirming and slipping out of his grip. He groaned. "Lady, quick, get the kids!"

Lady spoke to them, and they instantly pranced into the kitchen. She poked her head up the ladder. Benjamin and Jaime flew down and joined Marceline and Jake behind the couch.

Finn and Princess Bubblegum could be heard talking outside the door. Finn said, "Um, Princess, I know that Marceline is a vampire, but even she wouldn't sit in her house with all of the lights turned out. Are you sure that she wanted to have a jam session?"

"Of course, silly. Here, we'll let ourselves in."

The door creaked open, and Finn poked his head inside. Suddenly, the lights flashed on.

"SURPRISE!"

Finn grinned from ear to ear. "You guys! This is awesome."

Princess Bubblegum stepped in behind him. "Happy eighteenth birthday, Finn."

Benjamin flew up to Finn and wrapped his arms around his leg. "Happy birthday, daddy!"

Finn chuckled and picked Benjamin up, setting him up on his shoulders. "Thanks, little buddy." He smiled at the crowd. "All right guys, who's ready to party?!"

Everyone cheered, and so the celebration commenced. They ate, danced, and acted like overall party animals far into the night. Benjamin and his five cousins were put to bed before it got too late.

Later, Marceline managed to get Finn off the dance floor and lead him up to her room. He shakily climbed up the ladder, laughing and yelling like a drunk all the way. "Hey, Marcy, have you ever wondered if blue cheese comes from blue cows?" She didn't reply. Upon entering her room, Marceline turned off the light and shut the door. "Uh…Marceline, are you-" Finn was cut off when she slammed into him. They toppled off their feet onto Marceline's bed.

She leaned in and whispered in his ear, "You didn't forget our little deal, did you?"

There was a pause. "Man, I thought that you'd never cut to the chase."

She gave a low hiss and nuzzled him. "There's no turning back, hero. Are you sure that you we want this?"

He nodded. Without any further hesitation, she pulled his hat off and tossed it aside. She mashed her lips into his and ran her hands through his golden locks. He moaned quietly and slipped his hands into her back pockets. Her tongue snaked past his lips, and a battle for dominance ensued. Marceline won, as was normal for them.

Finn whined when she pulled away. She smirked and placed her mouth on his neck, licking and nibbling gently at his flesh. Finally, she latched onto his neck and started sucking. He groaned a little louder. She began gently grinding him. He still made noise, but he started dry humping her as well. As she fed, Finn took a hand out of her pocket and started reaching for the button of her pants. His hand trailed at her waistband.

Suddenly, the room was filled with light. Marceline detached herself from Finn with a smack of her lips. She hissed and whipped around to face the source of the interruption. Shaking, Benjamin stood in the doorway with an expression of utter horror. He flew past them down the ladder.

Finn held out his hand. "Benjamin, wait!"

Marceline gasped. "No, he wasn't supposed to see this! We need to go after him."

They untangled themselves from each other and jumped down the ladder.

"Ow…"

"Finn, you can't fly yet."

"Thanks, I know that now."