Lizard Dude:

Starting out with the provided line work, which i darkened slightly before adding a neutral tone to the background.

I then added in a base neutral brown to fill out the silhouette 

I repeated this with a darker tone for the armor plating.

Then i added in a light shadow by picking a softer variation of the darker tone, and adding a Gaussian blur to blend it in, before going darker and repeating this process with a gentler blur along the edges of the plates.

Using similar methods i began to add some tone into the softer fleshier areas.

I added a highlight onto the armor plating, before dragging in a snakeskin texture which i used to overlay over the fleshier areas.