At the first crack splitting the wall, Regulus stepped back, and back until he'd bumped into the other side and down the corridor some so there was proper distance between him and whatever was happening. And by the time the undead came smashing through the wall, Regulus had his wand out and pointing at unholy projectile.

And then he was gaping at the person who followed through the hole. Well, half a person.

"Huh- I guess that happens," he said.

He looked at the undead trying to gain its footing and then at the person now peaking through the wall, and though the danger was imminent, Regulus gave a curious nod to the new person.

"I believe it's your kill." Just how did this individual, blasting enemies through walls, dispatch one of the undead?