Thanks for the feedback. I'm sorry if you had trouble with the "retry" button. What the button needs to do is to retry the level and you start with the same number of skeletons you started that specific level. If you want all the skeletons, you need to restart from the beginning :)
The problem is that you do not start the level with the same amount. At least it didn't work for me. I was sent to the beginning of the level with the number of skeletons I had at the end of it.