It's very hard to read, you need to separate the different elements.
The path Mario stands on is very busy and saturated, if you desaturate+lighten+shift toward blue it would compete with his body less. Then you can lighten+saturate the cap, give him an outline at least on bottom edges.
The color of the sky and the lighting in general makes it seem like they're in a room.
Bowser's back foot combines with that spike and the fact that it's darker colored, makes it not look like his foot at all. If the sun is the light source why wouldn't it be subject to the same lighting as his other limbs? I see nothing to cast a shadow on it. And I'd raise or lower it to separate it from that spike.