Gumlee

Gumlee is the slash ship between Marshall Lee and Prince Gumball from the Adventure Time fandom.

Adventure Time
Depending on who tells the story, Prince Gumball and Marshall Lee's relationship differs. In the first original Ice King's rendition, the two didn't interact directly. In Marceline's rendition, they were exes, just like herself and Princess Bubblegum. (It's unknown if the reason of their break-up is the same as Marcy and Bubblegum). This interpretation becomes the canon relationship in the next Fionna and Cake stories by Ice King.

In Gunter's rendition (in the comics), they are close friends with cute interactions between each other.

Marshall Lee's relationship with Prince Gumball seems to be similar to Marceline and Princess Bubblegum's rivalry toward one another.

When Fionna and Gumball find Marshall Lee on the roof in "Bad Little Boy", they find Marshall was the one who had stolen Gumball's cream puffs. Marshall proceeds to drink the pink color out of a cream puff, then toss it at Gumball's head. When the puff hits him, Gumball's response is to grimace and begin climbing down from the roof, telling Fionna he is going inside and she can come with him if she would like "more polite company." It is unknown what happened to him after Fionna and Marshall Lee ditched him to go to a party.

Fionna & Cake
In the Fionna & Cake miniseries, everyone in Fionna-world have the memories of their previous magical lives erased. Therefore, Marshall Lee and Gary Prince (Gumball's human self) do not know each other despite being mutual friends with Fionna. One day, Fionna runs into Marshall and gets coffee on her uniform. She gets angry, because since she was fired that day, she had to give back the uniform and coffee is hard to wash. She also begs him to call his mom so she doesn't get kicked out of her appartment, which Marshall refuses because he has beef with his mother. Thought after eating one of Gary's cookie, he asks who made those. He finally accepts to help Fionna by telling her to seek Ellis P. instead of going to the vet.

A few days later, Gary goes to see Fionna so they can both buy ingredients for his bakery. Instead, he founds Fionna's appartment in shambles and Marshall out of the shower. Despite not remembering each other, Marshall flirts with Gary and tells him to calm out about Fionna's disappearance, as she is just doing her own thing like usual. That when she responds with text messages, confirming what he said. Gary decides to go alone, but Marshall asks him if he made the delicious cookies Fionna was carrying the other day. Gary confirms that he did and thanks him. The two goes out. Marshall slips out about his mother issues, and Gary tells him that he wants to impress the Lemoncarbs sisters so he can have enough money to open his own bakery. Marshall is impressed by that. They both spend the rest of the day hanging out together, until Gary opens his boss' bakery without her knowing. Marshall does something unexpected and secretly calls his mom to get to the Lemoncarbs. He tries to cancel the whole thing when he sees Gary being stressed out by the idea of actually confronting them, but it's too late. The sisters are unimpressed by the creations but Gary tells them that each character has a story. This doesn't do it for the Lemoncarbs, but Marshall genuinely wants to know more about his characters. So Gary tells him all about it.

Fanon
Gumlee has been shipped since the episode "Bad Little Boy" of the Adventure Time series. Since it's a genderbent version of Bubbleline, most fans assume that they had the exact same backstory. Though beetween the red laser at the end of "Fionna & Cake & Fionna" and the truth revealed in the episode "Prismo the Wishmaster" of the Fionna and Cake series, this might not be the case.

Fandom
FAN FICTION
 * Marshall Lee/Prince B. Gumball tag on FanFiction.Net
 * Marshall Lee/Prince B. Gumball tag on FanFiction.Net

Variations

 * Bubbline refers to the femslash ship between Princess Bubblegum and Marceline Abadeer