I can give an example. If something moves back in time, it interacts as if it has negative mass relative to us, who move forward in time. Of course nothing moves back in time but tachyons which exist only on paper. The worlds of things moving forward in time and backward in time never meet because they are just two different solutions to the same equation and we have absolutely no evidence that the second world exists. Inverted matter from Tenet should have received negative mass but we most likely will never see it because time may be an illusion likewise to rotation.

Well, i think some trouble lies in that things with 0 mass are already defined here. Light has 0 mass, and anything with 0 mass must move at the speed of light since it has no inertia to stop it. What other point of reference can we use when 0 has been so solidly defined?

No, the gravitational analogue of voltage is the gravitational potential energy. We can freely shift them by constants because absolute potentials are unobservable: only potential differences have physical consequences. Mass, like charge, is directly observable.