In the second image, you gave it an effect that I've been looking forward to see for a long while. Not exactly of a thunder, more of a mountain. I've got the image on my head, it wouldn't come out very well described.
The thudner effect you wanted may be with some clearer areas around the thunders. You know, the lightning. Instead of leaving only the white lines, perhaps making a somewhat darker path surroudind and following those same lines. My opinon, at least. I'm not very experienced at it either. <.<
Nonetheless, its really good, I'd say. You gotta teach me a few tricks on character designing...