- Show the total time it took to finish the game.
- Make each level have a max amount ( let's say 100 ) and it decreased by 1 every 10 seconds until you finish it. Once you finish it, your total score is increased by the amount left. The scoreboard would display this number.
As for medals, add anything really. I, personally, like medals that are a challenge to get. Maybe something like:
- Complete level [x] within [y] duration.
- Obtain a total score greater than or equal to [z].
The general ideas are just that -- ideas. If you think of anything better, or just don't want to implement it, that too is fine. Whatever tickles your fancy, really.