Finn came after the Ice King and ended up in their world. The ice king had kiddnaped Princess Bubblegum then Finn and Jake invaded the ice kindom. Killing all of his ice monsters and just simply throwing his penguins away, they saved Princess Bubblegum. Then the ice king reveled his vortex traviling tecnoligy, then when in after them greating Princess Buublegum a good bye.
As Finn prepared to leave the Princess as why he was leaving Finn qouted "I cannot let the ice king destroy another world, i must kill him"