Do not doubt this film's fabulousness. Doubt its credibility, maybe, but not its sheer power to amuse. But this posting is here to dispel some misinformation, not to review the movie. Suffice it to say, if you have a sense of irony and don't need MST3K to tell you what's funny, you'll enjoy it. About four scenes were taken directly from THE EXORCIST, but there were about a dozen movies that were much more derivative.
Actually, Warner Brothers lost their lawsuit in '78, but AIP didn't rerelease it out of fear of WB's corporate muscle, and because the EXORCIST craze was basically over with. I sometimes wonder if WB would have sued someone who was (or claimed to be) actually possessed during this period, as they seemed to think they had possession itself copyrighted. Listen closely: WB did not, and could not, order all prints destroyed. The movie simply went into limbo. It has been doing very well on bootleg video, and if the copyright holders (formerly AIP) wished to do so, they could find a good print and put it out on video legitamately, and rake in the dough.