The time when Finn and Jake teamed up with Marceline to defeat the Lich. It was a really intense battle. Finn showed great courage, Jake was there with his funny remarks and useful powers, and Marceline added her vampire - like strength. Together they managed to stop the Lich from causing destruction in the Land of Ooo.
One key moment was when they had deep conversations about their pasts. It brought them closer. Another was when they went on adventures together and relied on each other.
One key moment is when they first started working on a mystery together. That's when they really got to know each other on a deeper level. Another moment is when Jughead defended Betty against some of the mean - spirited rumors in town. Also, when Betty helped Jughead through his writer's block by inspiring him with her own ideas.
One memorable moment was when Marceline helped Ice King find his lost penguin. Ice King was really sad and Marceline used her powers to track it down. Another time was when they both got stuck in a magical maze. They had to work together to get out. They argued a lot at first but then realized they needed each other.
One important moment was when Simon was still in control of himself enough to interact meaningfully with Marceline. He would comfort her and they'd have conversations. Another moment was when Marceline saw the Ice King and was reminded of Simon, it showed how much she still cared. Also, the times when Simon would use his magic to protect Marceline were significant.
One memorable moment was when Finn made a big effort to win Princess Bubblegum's heart. He would bring her gifts from his adventures, like rare flowers or unique artifacts. Another was when he finally confessed his feelings to her, it was a really sweet and nerve - wracking moment.
The moment Finn decided to court Flame Princess seriously was important. Then, when they shared a kiss for the first time, it was a big step in their relationship. And when Flame Princess faced a crisis in ruling her kingdom and Finn stood by her side, it showed the depth of their connection.
The first time in fanfiction can vary greatly. Some fanfictions may portray it as a spontaneous moment full of passion. Others might show it as a more hesitant and gentle encounter. It depends on how the author wants to develop their characters. If the fanfiction is set in a particular storyline where they are facing challenges, this moment could also be a form of escapism for them within the story.
I'm not familiar with a character named Bronwyn in Adventure Time. It could be a very minor character or a name that is not part of the mainstream Adventure Time canon.