I've been thinking, again. If... heck, WHEN they make an AT game, it should be along the lines of Scott Pilgrim vs. The World. It could be 4-player co-op, with each character having different attacks. Fiin could use his sword, Jake could use his axe/stretchy powers, and you could have the other two characters change between levels. One could have Marceline, using her axe bass and vampire powers, Ice King, using his Ice Powers, a penguin guard, using multiple penguins and an ice axe, Susan Strong, fighting with kicks & punches, etc. There could little Bonus-y levels like riding LR, PB's swan, The Morrow, IK's beard to fight through the skies. And for a Sonic/Super Sonic nod, Finn could collect all the stars and transform into Super Finn(from Wizard). There could be power-ups in the form of power rings. It could be costumizable. You could use treasure as money. There could also be a map, so you could explore a little. The bosses could include The Lord of Evil, The Lich, Ice King, Lub-glub boss, etc. And it should roughly follow the storyline of the show, so that there could be a boss fight against Marceline in bat form(from Evicted!) and then build on F&J's relationship with her.
If anyone has any other ideas, shoot 'em at me.