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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
For the first bullet point, I pretty much assumed that health cannot go below 0 and accounted for it but there were no test cases when I submitted that had damage greater or equal to health. :/
+1 for all your other recommendations.