Zargos as Zargon instead of Nyx
by Marc SaindonThe Followers of Zargos are an evil group featured in the Milenian Empire sourcebook for the Hollow World. While Nyx is an immortal of Entropy, she's one of the tamer dark deities in that sphere. Instead, B4 the Lost City, could have its tendrils expanding into the Hollow World, having a few successful missionaries venturing into the Milenian Empire, establishing a cult, and its leader taking the title-name of 'Zargos' ("of Zargon" in mock-greek).
As magic and clerical powers are more difficult to access in the Hollow World because of the higher Attribute requirement, warlock pacts are really a tempting option for those who would seek magical power. Thus the Warlock pact of the Great Old Ones (patron: Zargon). They still organize themselves in a religion-like cult as the Followers of Zargos, but their goal is less about bringing eternal darkness to the HW, and more about releasing their 'god' from imprisonement. their logic is that if they have power now, they'll get even more power if Zargon is released (he'll probably just eat though, should that happen).
(art from: https://www.deviantart.com/forrestimel/art/The-Festival-428421287)