I didnt use lighter outlines, I used an opaque mask for the fire on the right.

The flame is angled right, it's supposed to be 'blowing' sideways on the sword. thats why the left is darker and 'behind' it and the right is lighter. 

I appreciate the tips, though.

If it's possible, don't use different resolutions at once. You can easily clear the edge of the sword, or make it saw-like, or anything like that. With these 2x sized pixels it's ugly and it's needless. And for a second suggestion: don't use lighter outlines than the item's own color, it looks bad, and also pointless. If you want it to count, color the upper outline to mimic the falmes' reflection.

Nice sword, but the flames seem to be behind the sword, i think they have to surround it instead.