These are some of the character design variations I produce based on the original concept sculpture:
The base sculpture for the different designs is done in ZBrush and it is pretty simple. Keeping everything loose and sketchy helps with the iteration process and prevents you from getting to attached to a particular design too quickly.
At the end, the sketch is not too different from the cleaner mesh I used for posting. However, I like to keep different versions as separate files throguth the process in case I want to go back to one specific design and recover a feature that I liked to incorporat it into the new desgin.