I do think it's Mugo. If you read again the chapter with the stairs that made Mugo's consciousness you can tell there's a fourth Mugo. Also, he's the one who told MC what to bring to avoid being eaten when he came of age (while Mugo and MC think it was Wise Mugo) and I believe that his presence was what made Mugo's scent change.
I believe he's the original, whole Mugo before whatever happened that made him split into the other personalities, and stayed hidden within the other Mugos till his lover got reincarnated and that's why the other personalities treat differently MC from other sacrifices: the Wise gave him his blood so he could avoid being devoured, the Jerk treated him unconsciously as his and the Monster thought he was the sweetest thing ever, so delicious he wants to "eat" him even if it hurts to try.
What's more, Jerk said that Monster is him so he knows what to do and that could mean they're probably beginning to bring forth their old self, the one who is all the Mugos.
At least this is what I think.
YOU-!! YOU ARE A GODDAMN GENIUS-- I NEED TO REREAD (fight my way through the sex) AND ANALYZE THROUGH UR LENSES HOLY SHITTT THIS MAKES SO MUCH SENSE- i cannot wait to see how this plays out bc i think u literally hit the nail on the head
this is very interesting! thank you for your insights, i might reread the series at some point and look for those clues! (๑•ㅂ•)و✧
I don't think the fourth guy is a Mugo, I think it could be a rival snake god/snake demon who went after Mugo's lover and manipulated him into betraying Mugo