The Odyssey is a timed "event" that has a set of maps that players must complete to get the rewards in the end. New Odysseys are available every few days and it requires an internet connection to download new Odysseys. There's a catch though; you only have one set of lives for the entire span of maps, and failing in one map means you have to start all over again from the first map. Harder difficulties give more cash and token rewards but they'll also have more maps to complete.