Moorecock Multiverse is good, but I can't think of anything they have on PRB.
Their lords of chao/law seemed universal at best. The beings who ate universes for breakfast are impressive, but not outside the scope of higher end Marvel cosmics, and PRB made even the most powerful look like an ant.
If the Black Sword (Which is supposed to be some kind of cosmic symbol or major demon? Not clear on the details, I only remember reading the Black Sword is far more then a simple common demon entity), tried ducking out PRB's soul, he'd simply send it away, or turn it into flowers or something.