Finn was trying to get Ice King to fight Fire Princess because he liked her.
Finn and Fire Princess break up, Finn meets some qt forest huntress wizard.
Finn finds his parents, his dad is a space adventurer, his mom was a nurse, all the humans went to live on an island and all the nurses got sick because some virus so Finns mom became an AI / took control of robots that look like her in order to take care of the humans.
Ice King gets a big backstory, his side story is what leads to the world almost ending.
Turns out the Crown was made in order to grant a wish, because a deadly comet was coming, the idea was whoever wore the crown would wish to be destroy the comment, The Ice Elemental made the crown, and had a pet dino named Gunter. Gunter wears the crown and wishes to be like the Ice Elemental instead of wishing to destroy the comet, so the comet hits and kills everyone, but the crown survived, turning whoever wears it into gunters idea of the ice elemental. So The Ice King found the crown and wore it to use its power to protect a child mareline from danger, the more he wore it the more he turned into the ice king. Eventually he turns all the way into the Ice King, his GF from the past time travels to the present and gets obsessed with curing hum / turning him back to normal. She summons the god of chaos who then eats Finn on the last episode.
Last Episode is giant war between candy kingdom and a new candy kingdom, made from princess gumballs child-uncle. But then evil demon god shows up and fucks everything up.https://www.youtube.com/watch?v=y5TkZ9bFodQ