Well, Mary Sues are definitely when you have to be confined for your own safety and the safety of others. (Unless you're 13 or 14, and then you get a bye. Not that we *read* the Mary Sue, no, but we understand that it's a symptom of early adolescence, not insanity, and wait for it to pass.) Crossover epics, especially the seriously crack-addled ones, are merely a sign that your loved ones need to watch you closely, because the crazy, she is a-comin'.

I can see Oz in pretty much any fandom.

Seriously? So you can see Oz in, like, Oz? Or Highlander? Or Good Omens? You must tell me more about this strange Oz-transfer ability of yours; I am profoundly curious.