Let's Draw Characters from Memory!
Remember the "Who Is Homer Simpson" Goldmine from 2008? Probably vaguely, if at all, but that's actually perfect, because this theme, like that one, involves faulty memory! The SA Goons attempt to draw cartoon/comic characters based entirely on their recollections, and the results look pretty comparable to the average deviantArt produced by someone who is, presumably, working from reference! In most cases, the Goons also include a from-reference version to demonstrate what they could do if not constrained by this concept. Some people find crude sketches charming and funny, others prefer higher-quality work: This time, there's something for everyone!
The Steak Justice
The idea is simple; draw characters without a reference picture to see how close you can get them. If it helps, you can follow it up with a from-reference drawing to gauge your artistic skill, especially if you don't have any like myself.
To get the ball rolling, I drew Philip J. Fry before and after looking at a reference picture, noting where I went wrong.
Just a Fish