I don’t have a character for my Mega Antagonist, can it be the sin that controls my regular Antagonist? Or will it be uninteresting if I don’t have a real, physical character to destroy?
Great question, and a common one.
The mega-antagonist must be a real “person.”
We need to be able to see the person rise and fall, succeed and fail.
As goes President Snow, so goes the Capital (The Hunger Games). As goes Mr. Potter, so goes big business (It’s a Wonderful Life).
You can get creative with what a “person” is, but it must be a real, nameable entity that has personal autonomy, creativity, discretion, and personality.
This is really true for each of the seven character functions. We need real characters that can be interacted with.
Some stories don’t make a lot of use of the Mega-Antagonist, he can just kind of hang around in the background of the story. But nonetheless, he must be there.