Well, the icon in general. xD
Im not sure what is that, but i think its a lighting or a "hame kame ha" thing. xD
Try to dont use the smudge tool so much, isnt a good tool really in the most of cases. There are many ways to get a thing like that without use the smudge.
A Tip: Use the Brush tool and takes advantage of all its features. Changing the Opacity and the size of the brush when you draw its that i do. And use a lot of layers, that helps and its useful when you edit your icon. I dont use GIMP so i dont know so much about it. But in photoshop you can add effect to specific layers, use those too.
About the icon, i suggest you to add some lighthings and some explosion at the end. I dont sure about that blue thing, maybe change its color to some more lighten.
Keep working m8!