Here on page 15 of the sketchbook is another unfinished pencil drawing, this time depicting Leonardo with his "new mutation" claws out -- at least on one hand.
As I look further at this sketch, I notice there is some texturing on his face, seemingly to indicate rough, scaly skin. Was this a consideration, to give Leo -- maybe even all the Turtles -- a slightly different basic look, with rougher, more reptilian skin? I can't remember... but it sure would have made them more time-consuming to draw!
There is also a slightly different arrangement for the straps which hold Leo's scabbards, as well as a belt which looks like it may have incorporated pouches or pockets of some kind. -- PL