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Day 12 is all about working towards the wheel pose. Like all challenges this isn't a one and done type of challenge. These stretches are going to need to be worked on and practiced til you can achieve wheel pose safely
Day 13 introduces you to inversions, so if you're working towards headstands then this is a great video for you to learn which areas of the body you need to tune up
There are many benefits to restorative yoga, not just for your mind but for your physical being too, and taking a day to relax and restore is a great way to end the series.