[The only reason that Rich doesn't burst out laughing at the sight of Batman is because of the situation. Right now they're facing a crisis and while it's impossible to tell if these little pocket dimensions have real, live people in them, he's not willing to take the risk.]

[But he still remembers that conversation he had when Hal Jordan was still around when they were walking around in the Hall of Justice museum in New Metropolis. They'd talked about Batman and Night Thrasher and talked about what they'd be like merged as one person. Potential names Rich'd come up with for their little crossover superhero: The Bat-Thrasher, Grimbat the Thrashman, and Night-Grim the Batslasher-Thrashman.]

[If they weren't in the middle of a crisis, he'd be having to fight down a giggle. As it stands, he's all business. (He'll have to have his giggle in secret later.)]

[So Bruce is greeted by the sight of a helmeted superhero joining up and warping a field of golden energy through the chokepoint. All of the zombies start moving more slowly, as if they're moving through molasses, and due to the incendiary aspect of his Nova powers, they suffer burns as they do it.]

It's a high yield gravimetric field. It'll burn them and increase their personal gravity. Slow 'em down.