This jam is specifically for games that feature depictions of mental health. The National Institute of Mental Health defines mental health as one's "emotional, psychological, and social well-being." They go on to state that it does not only refer to the presence of mental illness, and that being mentally healthy is "essential to your overall health and quality of life." How you decide to incorporate this concept into your game's narrative is entirely up to you, but if you're unfamiliar with the subject, we highly recommend researching further!
Previously-made characters, like any other asset, are allowed as long as you have the license to use them. In the case of fanmade content, that basically means... Does the creator give permission for the creation of fanwork? If the answer is yes, we have no issue with it. Just make sure to add credit where credit is due! We expect submissions like these to be non-commerical, so that's all it boils down to.