But there is little actual difference between Archons and Divines. Archons can't be members of the Pantheon of Solitude, and they are likely to be more scrutinized for any of their perceived ill actions. But overall, Archons are still Creators, and their place in Nym's Eye remains as equally vital to that of Divines.
The position and title of Undergod was made after the War of Eternity, though it is only ever referred to as a title by mortals; suggesting that it came much later. The Creators themselves rarely ever make mention of an Undergod, but it's mostly out of cautiousness. To mortals the title and position refers specifically to Gaerdras, who is the Creator who was imprisoned within the core of Nym.
The Undergod has no perceivable power, and he is used in the Faith of the Many Gods as a cautionary tale. Creators who dare to openly go against the Overgod or the Pantheon of Solitude might eventually suffer the same fate as Gaerdras, and become a god of powerlessness. Despite the fact that Archons fought alongside Gaerdras during the War of Eternity, only Gaerdras was made Undergod and severely punished after the War was won by the Divines.
There are still mortals who worship Gaerdras, though they must usually do so in secrecy. The Undercults are the largest of the hidden organizations who worship Gaerdras, though it is unclear whether he can actually hear or feel their worship. They make mention of the Undergod rising; speaking of prophecies that tell of how he will one day return, and reveal to his worshipers the true face of the gods.
The Undergod has remained within the core of Nym since the end of the War of Eternity, and few supposedly know anything about him, or whether his chains actually still hold him down.