This level was made for a contest hosted by bielles52 in which the contestants were allowed to only use assets from Megamans 1 and 3 and must include rush. I think only 3 or 4 people including me participated and someone else won. I tried to do this thing where you can jump from a slide out of a 1 tile gap and justified it with the inclusion of rush so you can just skip it.
I don't think this trick works anymore in 1.8 though.