You've already basically released your own character type into the public domain by creating that thread in which you instructed others to draw them, thereby releasing your own implied copyright. So now the concept belongs to everyone that wants to draw their own.
I have no problem with people making one of their own, thats the premise to Vexons. But even though they create their own Vexon doesn't mean they can run off and call it their own thing. I mean, im making them their very own character...if they dont appreciate that enough to not run off with my stuff then i dont know what im doing wrong here.
If people want to make their own game, go for it
If they want a fan fiction, go nuts...
I would just respect it if they would give me credit and call it a vexon.
I plan on having a forum somewhere where you can draw your own vexon and ill sprite it and put it in my game as long as the game is running, i take in ideas and a appreciate all of it.
Going off and stealing a vexon and calling it "shadow slasher" is on the same basis of Pirating "OF Rainbows" from Radio Head and saying "Fuck you Thom York!".
Im not saying anyone will or has stolen anything, im just saying it would be extremely unappreciative and stupid.