zeit 2 comes in the tradition of classic shoot'em up games and adds a time traveling mechanic, which extends the game experience in surprising ways. You can assist yourself by traveling back in time and co-op with your prior playing.
Time rewinding in zeit is not simply a way to undo things but an essential feature to beat the game. When initiating time travel, rewinding will continue until you either release the button or you run out of time-travel-energy. During that period your player and everything else on the screen is being rewound. As soon as you stop traveling back in time, the game starts playing forward and you are in control of the player again. While you are in the past there will be a ghost or shadow of your player that plays exactly like you did before. You are on the screen twice, as the normal player and a black version of it. Go back in time at the right moments to get the advantage over your enemies by having the doubled firepower that time traveling gives you. The time-travel-future mechanic lets you speed up the game at any time. While you are in time-travel-future all the points you score are doubled. This feature serves to improve score and pace the game when it feels slow for advanced players.