I like the direction the concept art is going, and the updated screenshot of the level: looks like you are in a deep furnace (OwlBoy's The Floating Continent - Lava music comes to mind lol)
The outline helps, but it seems like you are using a ton of colors in your sprite work for him. While I think it does look good, I've heard advice floating out there to not go crazy with all these different shades of color. I think the underlying principle (at least my rationale) is that it makes working quickly more difficult.
eg. Imagining you have to now make individual sprites for the run animation or jump animation. It's gonna be really tough to produce all of them at the same granular detail. And making quick updates will take time. I imagine starting simpler will be better for iteration.
