My headcanons after watching all Fionna and Cake episodes//
• Simon adopts Astrid as his own daughter and they used to make stories together
• Marceline invites Simon at her wedding with PB
• Simon renovating next beside to Astrid's house
• Simon will tell everything about his adventures with Fionna and Cake to Adult Finn, PB and Marceline (and they couldn't believe Simon what he has been trying to say)
• Fionna is having a long distance relationship with Simon or become as Pen Pals via texting with interdimensional phones (and thru telepathy); Simon realized that having a long distance with somebody wasn't so bad in order to stop being so clingy like he's always clinging into Betty before and they gotta rather enjoy themselves living their best lives
• DJ Flame got Female Fern pregnant
• Marshall Lee always buys Ice Cream Lady's ice creams
• Gary plays sudoku, othello, chess, snakes and ladders like any board games with Beatrice Butler at the Buttery Buns Bakery
• Gary and Marshall share beds and clothes together
• Cake and the Flying Squirrel hang out frequently
• Human Monochromicorn likes to pet Cake everytime Fionna and Cake visits at the Candy Store
• Minerva helped Simon checking is health daily then scanning throughout his mind and analyze the magic created along what's inside with a universe of F&C
• Farmworld Finn survives!
• Our Finn and Huntress Wizard plans to have a family
• Root Beer Guy and everyone in the bar singing Cheers intro with Simon
• Jay and Little Destiny having cute dates and tries to shoplift together on a shopping mall
• Hunter watches and stalks Fionna when she was nearby at the garden
• Fionna and Cake getting friendship bracelets made by dandelions, mixed-candy flavors and bubblegums
• Scarab enjoys Prismo's newly created fanfic stories
• Golbetty museum in Fionna's world
• MORE SHERMY AND BETH SKITS
• Finn visits Jake's grave with Marcy Simon PB, Lady Rainicorn and Jake's children
Praying to God that Fionna and Cake will gonna have a season 2 or more seasons to come because there's alot of cliffhangers and feel this story isn't clearly done. It's just the end of one character arc within Simon.