I wanted the fireball to look like it was moving, so I started by applying a sine function
To make it look like there are some actual flames, I added some quintic smoothed FBM
Then I used a lerp on a step function on radius to get a cell-shading effect
The upper and lower ends of the range were getting cut off, so I added some bias and gain functions to tweak the color bins and the palette
I didn't like that the center of the ball just looks like a yellow ball. So I lerped with perlin noise on the lowest bar of the histogram.
Finally, for some contrast I put in a simple background.
