User blog comment:27finnsprincess/Season Finale Predictions!/@comment-5391523-20120922022217

I think that the Lich was a human that was convinced by a demon to acquire immortality, in exchange, the human would exclude his soul for the sake of the trade, he turns into an evil being and has the desire to destroy Ooo because he's afraid for what the humans have done to Earth after the Mushroom War, so he wants to kill everyone, to this, he locks everyone in his Bag of Holding and throws the Bag into the sun. Or he's just an evil being cuz' he got a malignant consience after turning into the Lich.

But, back to the topic, i think that the battle will happen just like in the comic books, the Lich will bring them to the Bag of Holding, they'll get out of there and, then Finn&Jake will team up with everyone and fight the Lich.