Yep, according to the Monster Manual you can't have a fiendish incorporeal creature...but this class could simply exist as an exception.
Apart from that confusion I like it. I watch quite a lot of Abridged anime and on more than one occasion I have head something along the lines of someone being possessed and saying "We are 4Kids and we are many. Now we fight on". Heheheh.
Edit: What no Demodands?