I will add my own suggestions, feel free to add your viewpoint to have a more challengeing event.

-Earn Hattricks x3?
-Clean sheets x3-5
-Score with a sub'
-Earn a red card?
-Heal a injury

Top Scorer? Rated? Assists with points rewarded?
Supercup or other seasonal targets as mission to earn points. (ex: Reach top 2, win the cup, win the top scorer = 100 points)