Please help make a tier-0 class. You'll see what I mean.

[Zeta Kai]

You want an arbitrarily powerful BBEG that does not need progression up to epic levels, using a class that will never be taken by a player, and you already know what you want him to be able to do? From what I can tell, all you want is a homebrewed monster that's also a human. Just fill out the stat block with abilities.

That would the most simple solution, admittedly. It's not like this is gonna seen by the players. That's kinda a 4E approach, whereas the 3E in me begs to have a class progression. A weakness, to be sure, but there it is.