Starting at council level 12, you will be able to play a Master Mission in every round of the Challenge. It is a higher difficulty mission (+6) that will allow you to skip the entire round. The number of stars that you score on the Master Mission will apply to all of the missions in that round (e.g. if you score 3 stars, you get 18 stars for the round).

 

The map in the Master Mission will begin with the first map in the challenge, and rotate to the next one every round you pass. 

 

Note: The Master Mission will cost double the amount of Gas of a normal challenge mission. Moreover, the Master Mission can be replayed and you can also go back to the normal missions too, for example, score higher on some.