Completing all the challenges in a level unlocks a harder mode of the same level, complete with its own objectives. Completing each level’s challenges is very difficult and sometimes nearly impossible to do all in one pass. Instead of trying to do multiple challenges in one pass, do each challenge individually. This is much more efficient, instead of trying to do them all at once and dying over and over. However, the two objectives that require you to destroy a certain percentage of enemy forces can be done in one go.