Although the whole "you're not the first" makes sense for everyone up until Elpuri gets beaten (also accounting for bones) I'm going to have to agree that it seems awful strange that the big baddies you got through before have resurrected. Still, having Petrus say "you're not the first" or some variation thereof would be nice, and I'd be willing to overlook the other small details. Maybe you could work in Oree here - I'll get to that later.
However, having him rattle off a list is going to be a problem - both in-universe and code-wise. I think Somagu's right in that Petrus would likely not give a damn about all the slaves that get sent to him for a suicide mission on Elpuri, and then having to display what is effectively the hi-score board is going to be both a problem to code and perhaps an unneeded distraction.
I do like the idea of a successful high-priest victory replacing Petrus with the previous protagonist, and yeah you could easily resurrect Elpuri under the guise of "Oh he comes back every couple of years". Or perhaps say that it's to do with Oree who gets resurrected every few years (would make more sense) and in turn resurrects Elpuri and all the other baddies. Kinda like Castlevania's Dracula except the protagonist turns into a iron-fist dictator when he wins.
You're right about the hierarchy of Attnam - the High Priest rules over all and is replaced by whoever can beat him. Kinda like that Riddick movie.
As for a Champion Victory you could have the previous champion replace whoever the head-guard was with the illithium armor.
The only problem I see with this is having to code it as you'll have to save the last successful players somewhere. Setting a flag to trip for successful characters will be easy enough, I'm just not entirely sure how to go about loading past character data from a file and then having them replace Petrus/Head Guard.
A female character would be troublesome storywise too because, well, you're a banana grower at the start and all the banana growers are male. Then again, you are said to be an outsider raised by hippos so I can see that working in just fine. If we were lazy we could just make a separate chest sprite with a bra on it and call it a day.
Somagu wrote
I can think of one other less tasteful place to put the beard instead...
I for one would be in support of gigantic armpit-beards.