Rather than "softening", this piece mainly just needs
clean-up. Here's a clean-up of one of the frames:
I made the lines smooth by reducing their thickness, got rid of some unneeded colours, and made the curves smoother by getting rid of jaggies. I also made the flames a bit more consistent by making them yellow near their source/core, and red (cooler) away from the source.
I also changed a few of the shadows and highlights to be a bit more consistent with each other. It's better to avoid highlights that look like lines, they rarely help give your work form.
I recommend doing your own clean-up, since you know better than I do what the creature is meant to look like. I had to guess based on the rough lines and shadows, and in many parts, I wasn't sure what you intended.