[quote=@Dead Cruiser]
[@dragonmancer]My idea for the "eldest" thing is that he remembers a time before any of the other (currently present) gods existed. Something like a "first generation" god, and is perhaps the last member of their kin.

The omnipotence would work exactly like this: he knows everything. He doesn't know the future, but every piece of information that currently exists in the world is in his possession.

Though he's generally an observer, he takes action when he deems it necessary, and acts swiftly and decisively. Perhaps at some point in the past he acted by "taking the mind" of another god, essentially lobotomizing them.
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Its a good idea, but I have a few issues with it. 

#1. While I like the idea of a different generations of Gods, like the titans to the Olympians or the giants to the Nordic gods, If there is multiple generations including the 'elder' gods, I would prefer if your character wouldn't be the only one of this category. In fact before we get started I'd like to appoint several other Gods in this possession to perform something similar to a triad or the big three Gods, which of course Your God would likely be apart of.

#2. Knowing every single bit of information, including about what the Gods are doing is stretching a bit into too much power in one mind, being able to shut down other Gods, at any point, I'm going to have to turn down completely. That isn't to say you could defeat a god (I will be including a certain element that can neutralize gods to some extant), but the method you proposed isn't gonna fly, unless if you were to balance it to where it would only be possible in a very planned and calculative method, prone to backfire if it fails either by failed execution or the target was able to avoid it, and that the method isn't a permanent way to deal with a God, rather a temporary solution or a temporary seal. 

#3. I can allow some form of semi-omnipotence, where he can basically know all of the general information (Not specific information or detail mind you, unless if he were to investigate upon one instance or another personally.) of the present in the earthly realm, but that's as much as I can allow. The mortal world is like the playground to the Gods, so I can allow such a world to be easily exploited, however I'd prefer if you and every other God didn't have the level of omnipotence where they knew about everything of the other Gods were doing, especially since I'd like to install conflict with each God, so as far as what your god would know to the other Gods at what their doing in each moment is limited if and what the Gods are doing in the physical realm as physical manifestations.