How to torture a physics student: set an assignment that goes "write a minimal extension to current physics that is maximally consistent with these comic book panels as shown, treating them as reasonably accurate annotated illustrations of real world events.
That's more fun than pointing out individual inconsistencies with the real world (for instance, never mind how Batman eats, how does he drink, how does he breathe?), and allows for a small amount of wiggle-room in that one might propose tests to disambiguate or bound some of the claims made in the text or to raise questions about the accuracy of the illustrations in quantifying movement, colour, etc.
Just coming up with ideas to try to explain the nature of the "force" surrounding zebra-Batman in the first few panels is actually really hard.
I think the hardest thing here is with respect to inertial mass. This force is apparently non-Newtonian. Objects with much more intrinsic mass than ordinary-Batman (a tree! a lamppost!) are seen being accelerated away at substantial velocity from Batman, but Batman appears to be stationary with respect to the surface of the Earth. He also isn't compactified into a ball in the large panel on page 8 as everything around him is pushed away. Moreover, as you noticed, Batman is not accelerated away from the Earth's surface.
However, there's the glow and some arcing in these panels, and we could work with multiple forces rather than just one...
As you note, repulsive force can't be electric because things in the environment are (or rapidly become) electrically neutral at large (i.e., human-sized, tree-sized...) scales. The objects accelerated away from zebra-Batman are sufficiently varied to preclude magnetic interactions too.