Ao is not the Overdeity of all of this (each multiverse has an Overpower, apparently). Lumi is the ultimate being of all of this, however. Dunno what that'd mean for him, if a tier change is even needed aside from him being infinitely and transcendentally superior to a High 2-A
Each overpower has only one universe, which are also known as "spheres" or crystal spheres. Spheres can contain anything from a single planet with a moon and a sun, a solar system, a galaxy, or many galaxies, or even an "infinite" plane world. A sphere with its own local version of the exterior planes (parallel, inner, outer, what have you) is a multiverse. (As mentioned in an earlier post, the exterior planes are all shared by all spheres at the same time, but have local manifestations for each sphere, inhabited by the local versions of the gods, demons, etc).
Ao have two spheres (Abeir and Toril). But that is rather an exception to the rule.
All spheres exists within the Material Plane, and the MP is enveloped by the exterior planes. Some editions have the concept of multiple MPs, but is not explained if there are multiple versions of the planes beyond the Material or if all multiple MPs share the same planes.
Also, each overpower has control over one pantheon, but they can only control the "aspects" of their deities within their spheres. Not all gods are multi-spheric, tho.
Within the context of a thread, would all of his opponents not originate from beyond his domain? Seems pretty crippling.
Nope, because in D&D being able to trespass the shell of a sphere is quite the feat. Gods cannot, by raw power, do that. The shells are hard enough to withstand the Phlogiston (raw energy of creation). So, if you want to attack Ao you either need to be inside his sphere (where he is stronger than anything) or by incredibly powerful to do something not even greater deities can (breach the shell of a crystal sphere).
An overpower cannot control a being from other sphere, that its true. But they by no means are totally weak against them. They just have not total control over them, unlike with beings that are from their sphere.
So Ao literally can't be fought unless they originate within the Forgotten Realms
No, he can be fought. He will be just not all-powerful against this individual. As I said in my example, while Ao can crush Toril's Demogorgon just by thinking it (regardless of how powerful Toril's Demogorgon can be), he would have to actually fight against Oerth's Demogorgon, and have chances of either losing or wining (nor an insta-win).
This happens in Dragonlance, for instance, when High God (the overpower of Krynn) had to fight Chaos (a god that comes from the void from which the High God created the universe—something outside Krynn's sphere).
Though the living planet thing may be interesting.
Good ol' Allabar. I can bring its stats, if needed.
