Originally Posted by Mr Magic
Do you have to complete each challenge in one playthrough of that map? Or can you replay the map to get the one's you missed?
You can replay the ones you have missed but you have to start from WAVE 1 all over again which really sucks big time.
Imagine you try challenge/wave 15 and you die/fail then you have to restart from wave 1 all the way to the end and try it again!