Holy cow.
After 871 deaths, I finally finished 7C. That was amazingly difficult--and even harder than it looks on the videos. So many of the moves require you to be in an surprisingly exact position--hitting the pistons, dodging or falling through the crystals, tagging the tiny wall kick. The beginning of the final crystal maze almost had me stumped before I realized you have to be near the top of the horizontal corridor in addition to near the left of the vertical corridor.
To make things even crazier--after I talked to the old woman, I set down the controller for a second. When I picked it up again, I jostled the button and dashed off the cliff. Somehow I had enough composure to dash back, climb up, and recover the heart. But man, I would have been tilted if I had come so far to die at the final cliff for nothing.
8C remains and then... it's over...