I've done this once before and found it really enjoyable, it's also great practice as I want to improve my character design skills, so if anyone has an original character or creature in mind that they want me to draw for them, just post a description in the comments and I'll see what I can do over the coming days/weeks/months! :)
Apologies in advance If I don't get to your request, my focus can shift really quickly but I may come back to it later on.
Here are some examples of previous requests.