Wow
I admire your use and knowledge of fbf. I personally mix them up, since tweening can help so much at times. Reminded me of Brackenwood styled setting, but your style is definitely there. The backgrounds, water effects, drawings, and animation were well done.
The sound was appropriate, but the grunting could have been tweaked, mainly when he fell off the mountain.
You can tell a good story too, because when Sisyphus finally made it, I actually felt happy for him. You also know where to put humor in, even though this was sort of a punishment in the original myth. You took a damned person and turned it into a lighthearted comedy, which I commend you for
So overall, great animation and drawings, original story , decent sound, and all at 14! Fantastic job.