So if you could have anybody as a guest star NPC who would you have? I'd have Quagmire from Family Guy just outside the Chamber Of The Princess. The only thing he would sell would be humanity for 1,000,000 souls and if you're mad enough to try and buy one at that price he would say "No way man,do you know what these look like? do you know what I use them for?" If you talk to him he would say "Amazing chest ahead" and "Try holding with both hands" And when you talk to the Pricess he would be saying "Giggitty giggitty" in the background.
Ostrava of Boletaria. He'd help you fight the red dragon on the bridge, though probably not very well. He'd also appear at random points with dialogue relating to the lore. --- "invade some poor sap and jihad bomb him" - LazyKenny