Nice job on this one! I found it through the 20 Games Challenge list.
First, I love the colors overall, they are a bit bright, but they work well together. The Mushroom contrasts well with the background. I like the parallax a lot as well.
As for the mechanics, the jumping takes a bit of getting used to. For platformers like this, I think I'm used to the character having a bit of momentum left over when I stop holding a direction, so I missed a lot of platforms/enemies by just a little bit because I think I kept feeling like I'd continue just a bit farther. Once I got the hang of it, it wasn't too big an issue, but it did trip me up occasionally. (Not sure if that's the actual issue, maybe I'm just bad at these.)
While I do like the general motif for the music, it did get repetitive quickly and I ended up turning it down. It's a good start for an idea though, I think it fits the mood very well.
The "D" hint when getting the fire wasn't immediately clear to me, but of course the fire was very fun.
I also would have liked automatically continuing to the next level, but not a big deal.
Nice subversion having the main character be a mushroom, that gave me a laugh. Nice work.