*Warning! The following contains more in-depth details about the _Adventure Time_ finale "Come Along With Me." *
Adventure Time's finale had a couple big moments for viewers, with one fan theory getting confirmed in a pretty big way. It's been speculated for a while now that Marceline and Princess Bubblegum had some sort of romantic relationship, although the show was never too blatant in displaying it to viewers. That changed in "Come Along With Me," when the two kissed after Marceline believed Bubblegum was gravely injured. Executive producer and showrunner Adam Muto explained how the scene came about, and how the kiss wasn't initially in the script:
There was some conversation about [logistics], but it was really up to [Hanna K. Nyströmthe], the storyboard artist who got that scene, to decide what her take on it was going to be. It actually wasn't in the outline when it was submitted. It didn't say that they kiss. It just said they 'have a moment.' When Hanna boarded that, there was a little note in the margin that said 'Come on!' with a big exclamation point. That was the only note. I can't argue with that.
Eventually, Adam Muto and the Adventure Time team decided to approve the kiss for the finale, and Hanna K. Nyströmthe gets the credit for the iconic moment. Part of the credit, anyway, as Muto added that the two's dynamic would've never gotten to that level had it not been for former writer for the show and Steven Universe creator Rebecca Sugar laying so much of the groundwork that made the kiss possible. Muto told TVLine a kiss between the two had been an "ongoing conversation," but that it was never in the show's original pitch to have something like that happen.
Once it was decided a kiss between Marceline and Princess Bubblegum was going to happen, Adam Muto and the Adventure Time crew had to do some soul searching as to how to go about it. After all, seeing two members of the same sex kissing was always going to be a talking point, and those involved didn't want the kiss to overshadow the finale as a whole. Muto explained the process the team went through in debating the scene's inclusion, and how they ultimately made the decision:
We knew that if we put this in, it would get some attention. But would it be too much attention? ... Or would we be downplaying it too much? We knew we wanted to incorporate it, and in the end, you just have no control over how people will remember things.
Adam Muto didn't lay out Marceline and Princess Bubblegum's fictional futures post-Adventure Time, but said fans can watch the kiss and "construct what their life will be like going forward." Whether Muto is being cryptic about the future of the characters in case there's any chance of a spinoff down the line is unknown, although nothing has indicated that beyond the introduction of Shermy and Beth. One could speculate Bubblegum and Marceline wouldn't be around that far into the future anyway, although with Marceline being a vampire and Bubblegum being, well, bubblegum, who's to say they aren't still kicking around deep into the future?