>This was Finn’s childhood and on the cusp of becoming a good adult. Hopefully he’s a learned a lot and become a more complete person. He doesn’t even have a sword through most of the finale at all. The idea of him putting down a weapon as the way to resolve a larger conflict ... this won’t help in the situation. I think that was an important thing, not trying to show that.

>That’s also why The Lich didn’t come back as a villain. His story felt like it was over. if he came back again, it would feel like Skeletor — this evil that had to be defeated over and over again. If you can always defeat something and the day will be saved, it’s not as satisfying as something you can’t defeat — this thing that you can’t actually deal with in a direct way.

https://www.polygon.com/tv/2018/9/3/17806570/adventure-time-finale-finn-bubblegum-marceline-adam-muto-interview

You guys didn't want a final climatic battle between good and evil did you? I mean, Adam Muto says you wouldn't have liked seeing Finn have a grand adventure involving him having a final triumphant fight with the Lich, showing Finn adventuring and fighting and over-coming obstacles? He's grown apparently and now no longer needs or wants to fight like he used to! That'd be too much like He-Man and Skeletor! We didn't want that did we? We didn't want this to become Legend of Zelda now?