Ah, now a matoran moc, be that a matoran form of your self-moc or just a matoran moc, I can definitely say is fine. Plannin' to make myself one sometime.
Really, I don't even think there has to be a limit on self-moc's unless you want there to be.
I... um, I have to say it's probably shadow, but mainly an AU-ish version of mine. (Really, multiple of my mocs have some form of made-up element or just don't have one.)