How do I beat 'Journey of the Prairie King' in multiplayer?
As of 1.5, you can finish the game in multiplayer.
Finishing "Journey of the Prairie King" is now possible in multiplayer due to the option to save your progress and resume the game at a later time. So you may complete it in multiple sessions.
Whereas before 1.5 you could not finish it because one maximum-length game-day (20 hours) passes in real-time in 14 minutes 20 seconds and a complete run takes about 20 minutes if played optimally.