Get all the money of level 1 to unlock
Get all the money of level 2 to unlock
Get all the money of level 3 to unlock
Get all the money of level 4 to unlock
Get all the money of level 5 to unlock (it's impossible, don't even think to try) => Just For Aliens
Finish level 1 without dying to unlock
Finish level 2 without dying to unlock
Finish level 3 without dying to unlock
Finish level 4 without dying to unlock
Finish level 5 without dying to unlock (it's impossible, don't even think to try) => Just For Aliens