"Goodbye Marceline" is the 5th episode of season 3 of Adventure Time Origins and the 31st episode in all.
Simon and Marceline were wandering through the wreckage of the world when they arrived at the house where Marceline lived before the destruction of the world. When they entered the house Marceline ran upstairs to get something, Simon on the other hand looked around in the house, he saw family pictures of Marceline and her family. Simon saw that she had parents and a sister, but the face of the mother was ripped. Simon continued searching for a good picture of the mother, he eventually found a broken photoframe on the ground containing a picture of the mother, he saw two big fangs, indicating she was a vampire.
Marceline came downstairs with a note and gave it to Simon. She told him it contained the way to open the Nightosphere but she couldn't read yet. Simon said her to draw a happy (phil) face and douse it with bug milk. Marceline did as he said and Simon chanted a Latin spell which opened the Nightosphere. Upon arrival Simon looked around with Marcy on his shoulders, but suddenly they got attacked by many demons. Simon tried to fight them off but couldn't win. He didn't want to use his ice powers which caused Marceline to be dragged away. Simon tried to get her back but quickly lost sight of her. Marceline was thrown into her chamber.
Simon travelled through the place and eventually found the chamber where Hunson, the father of Marceline, was. Hunson thanked him for taking care of Marceline but said his job was done and he was not needed anymore. Hunson wanted to suck his soul out but Simon decided to use his ice powers. The two fought each other meanwhile Marceline escaped from her chamber using her vampire abilities for the first time, as thought by her mother, she headed to her father's room and stopped the fight. Simon was promised to escape so Simon and Marcy said their goodbye, but when saying goodbye Simon suddenly didn't seem to remember Marceline anymore. Marceline cried and Hunson sent Simon back to Earth. After that Hunson punished Marceline as she had to stay in the Nightosphere, Simon continued his wandering on Earth without his memory.
- Dark Princess
- Marsha (mentioned, photo, flashback)
- Rose Abadeer (mentioned, photo)
- Dark Overlord (mentioned)
- This is the first encounter of Hunson Abadeer and Simon Petrikov.