A tough platformer and an excellent entry for the jam! That shadow is a crafty one, couldn't quite outsmart it but I ended up with four of the five(?) gems. I love that each gem feels like you hid them behind an intentional platforming puzzle instead of at random. Gives each one their own unique challenge to obtain.
You have a lot of potential to go many ways with this idea, my suggestions are to maybe include some sort of progress indicator (maybe silhouettes of uncollected gems in a UI somewhere that fill up or color as you collect them) and to maybe reduce some of the difficulty on some of the jumps. However, take the latter with a grain of salt, my platforming abilities may just not be up to par!
Keep it up, this is a solid and fun submission!