Above is the original sketch for Level 04: Lava. Below is the revised version. I replaced the “rotating platforms” on the left with more natural looking fragile rocks. This revision not only blends in more with the environment, but it also adds extra challenge after the Mine Kart jump as those rocks break as soon as you land on them. I further replaced that floating brick pillar (top centre) with a more natural “floating/tilting” rock (assuming that floating/tilting rocks are perfectly natural that is!). I also cleaned up that area due it looking clustered. I widened the final climb on the right.
With a note to Chris’ fill technique, I think it would be great if the colour was the lava and as you were running up the hill, it would chase you and fill the level at the same time!