Okay, I've mulled it over for a while (many thanks to the guys at the Keenspot forum), and here's what I think:
The guy in the short cape is the Mastermind of 2/18/05. His immediate goal is to resurrect himself.
I don't think he's the sorcerer who created the Dewitchery Diamond. The diamond is of medieval origin, and, frankly, Mastermind's pants don't look medieval. (Yeah, I know he could have shopped since then.) That may be a thin thread to hang my theory on, but I'm sticking to it.
I don't think he's directly related to Nioi and Lord Tedd. At least, we have no reason to believe he is at this point.
But I think he is taking advantage of the mental breakdown and confusion Ellen is experiencing as a result of Nioi's nose-beepage dreams.
Dan has told us that Elliot used to wear a different hairstyle. That style looks like the one worn by the 6/6/05 figure.
On that basis, I agree with those who think that the Mastermind is the same as Elliot's Inner Demon. (I'd like to ask Greg if Elliot has more than one.)
It seems that for some reason, Mastermind/Inner Demon needs Elliot to be in female V5 form in order to resurrect. I have no idea why.
I don't think it has anything to do with pregnancy.
But if it does, you'd think he'd at least wait until Elliot graduated from high school. Sheesh!
M/ID was the mysterious cause of the TF gun's malfunction, and the cause of Tedd's momentary anger at Elliot.
Hence M/ID calling himself Ellen's "father."
M/ID temporarily possessed f-Elliot on 6/25/02, making him growl "Grrrrrr."
Perhaps to resurrect, he needs Elliot to be female, and have his ki energy in fighting mode.
Perhaps M/ID wants Ellen both to transform Elliot and then to pick a fight with him?
BTW, I think that in 6/6/05 panels 1-3, M/ID is talking to himself, and in panels 4-5, he begins addressing Ellen.
Perhaps M/ID wants to possess f-Elliot, as he did for a moment on 6/25/02. But why can't he just possess m-Elliot in order to resurrect? What's the diff?
Or is this like the Tedd's-cooking thing?
And where do the immortal forgetful "French students" fit in?