Unlife Vortex Guardian

[wraithstrike]

I am running AoW in Eberron, and I still use the 3.5 Lords of the Nine, except for the guy that is trapped in Ice, and Demond Lords. I want to use the avatar of them as a guardian for the Unlife Vortex. In return for helping Kyuss the Devil/Demon will get a large number of souls or whatever else Kyuss might agree too. The issue is that I don't know which one to choose. I think Orcus may try to take over, and he may not want Kyuss gaining that sort of power since it may take away from his undead powerbase.
Suggestions?

PS:Orcus is still an option with a good enough deal.

[Mewzero_hgc]

Lashonna may already have some connections with Mephistopheles, thanks to the Artifact that controls the Blessed Angels.

Instead of souls, the Devil/Demon might be interested in discovering details about the ritual Kyuss used to become a god, or even be interested in what happens with the Monolith after Kyuss is freed. Maybe it might be used to imprison another Demigod or powerful Devil/Demon. Mephistopheles might want the vacant Monolith to trap Asmodeus and try to take over Baator, for example.

In my campaign, I'll have the Unlife Vortex being powered by an Evolved Horrific Vasuthant(Monster Manual III, p. 182-183) that is also working as an undead uterus for an Advanced Atropal Scion(Libris Mortis, p. 84-85), probably gestalted with some levels of Psion and Chronorebel for more action economy shenanigans, since it will face the party alone after the Unlife Vortex is destroyed.

[wraithstrike]

The details on the creation of the monolith or the monolith itself would be a nice prize. I think I will look into that. Thanks.