Essentially, it's a short video tutorial that teaches how to climb up the chimney-looking tunnel that leads up to the chamber where the Difficults are with all characters.

Note: With Dustkid you must double jump initially to grapple onto that first inclination and then double jump again when leaping into the chimney.

I initially posted this on /r/Dustforce and you can find this thread here: http://dd.reddit.com/r/dustforce/comments/15w9kn/video_tutorial_climbing_up_the_chimney_to_the/