I want to stop him. I want to stop this. I want him to stop. I want--
Billy threw his hands out to his sides just as the blue lights started to swell from his palms. He was absolutely terrified of trying to inhibit Magneto's powers, so he couldn't physically refrain him; couldn't interfere with the grip that he had on the building's skeleton of the metal objects in his room, but he could move him, he could move them both. He could put him somewhere without any metal so they could talk about how no, nothing is getting decimated and no, he can't just destroy the tower whenever he feels like it.
Unfortunately for Billy, the last movie he watched was the sequel to How to Train Your Dragon, so the place that they were moved to, the place he instantly, accidentally created, was a clearing in the woods. A valley with high cliffs on all sides. It was night, the sky above them burning with a million stars, visible once the bright blue light that Billy had engulfed them with started to fade.
"Well. Here." He said as he exhausted, looking around himself with as much awe as anyone who had no idea what was happening might. "Here-here we are. Decimate whatever you want."