Hi lilwing, welcome back
This is kind of a tough one to crit, as the original Plok sprite is total crap. Of all the pieces of lineart to base your work, I would never have picked this one! However, if you're set on it, the main things I would work on is including brighter reds, increasing the amount of contrast (note the original's use of dark outlines to achieve this - not the only method of course), making the eyes more round, and adding details and definition to the character, even if its not explicitly defined in the original.
Also, it should be noted that your coloration makes Plok look a bit the S&M gimp; if this is not intentional you may want to avoid using a skintone on the body and upper arms!
