The crab model is from Truong CG Artist gumroad store. I retopo the model to be more optimized. I then adjusted the UV map. The UV map has a lot of seams to ensure that there is as little as possible texture stretching.
I usually start texturing by having an average colour, then adding variation of a max and min value of that colour with grunge maps. Then I usually layer everything else I want to be shown on the textures from there. At a certain point I realized the red wasn't as bright and didn't pop when you looked at it, so I increased the saturation and brightness and then I had to dirty up the crab a bit, so I started adding some sand in the cavity areas. Also because this was quite stylized I thought I could make use of SSS to add some personality to the crab and make it a little cuter by having a more intense SSS areas near the face and eyes.
Marmoset Scene