Given what I started with, I think it came out rather well.
Here's the original line art:
The behemoth is based on several things: the estemmenosuchids of the Middle Permian, the Behemoth in Blake's illustrations to Job, these weird green dog/lion statuettes my Granny kept in her living room, and a vicious chihuahua named Paco who used to get into my backyard to terrorize my children. (Not that you wanted to know all that.)
I began by creating a layer of colored flats to provide the base color for the image.
Then came the fun part: adding tone and special effects. Here's the final image, sans line art:
I think it's pretty cool-looking like that, a bit like a Frazetta painting (if I do say so myself).
And now let's see that final image one more time: