The most important thing to remember is that this image MUST fit cleanly inside the facebook square. Therefore, I do not require a full body for the mascot, but I do require a very detailed head with clean lines. Also, since my company name is very long, you do not need to incorporate it into the logo, either.
Some important details about the mascots features: I'd like to "suggest"/incorporate/drive home the point of my company name by using a rock in an action position for one of the mascot's eyes. You can also use glasses similar to the zombie designer image (if you prefer) and have the rock lodged into one of the lens and the other eye can be wide open or closed.
The other detail is that, since this character will be providing tips and expert advice about windshield repair, the lumps and bruises he has taken over the years, need to suggest a bit of wisdom rather than horror. But I don't want a smiling character, I think the zombie designer character captures this idea I'm after nicely, but you are free to make up your own expression for him as long as it works!
I prefer a medium outline in black to thin lines. Also, winning designs will provide interesting shapes for the face to fit inside/on, a boring realistic circle won't inspire me.
Finally, every color is up to you. But remember than realistic anything isn't what I'm after. If you think lime green would be a great color for the mascots eyebrows, do it. That's what I am looking for, out of the box thinking. The only caveat is that you be judicious with your accent colors: im not looking for clown makeup.