The AP I'm trying to write at the moment features Rakshasa as a recurring theme. The final BBEG is going to be Ravana, one of the "super-" Maharaja. I may even make him mythic; we'll see. The PCs shouldn't even know about the Rakshasa involvement/conspiracy until level 8 or 9 (of approximately 15). The beast-headed baddies are really, seriously twisted horrors and I intend for them to be eerie and terrifying. Good times.