One of several changes director Bryan Singer made to Matthew Vaughn’s original Days of Future Past script was change the Magneto prison escape scene. In the original treatment of the script X-Men: First Class director Matthew Vaughn was actually going to have a young Juggernaut smash in and help Magneto escape not Quicksilver. While speaking with Empire Magazine the former director talks about how the scene was originally gonna happen:
“I had Juggernaut being thrown out of a plane at 20,000 feet and using his head to go down a hole to get to the bottom of [The White House]. I had Beast saying, ‘I have a plan,’ and him replying, ‘What’s the plan? What’s the plan?’, and they go higher and higher and Beast was going to go, ‘This is it!’ and chuck him out the window. Then he goes smashing through [The White House] with his and Magneto goes, ‘Who the fuck are you?”
He does go onto admit Bryan Singer changing the scene to Quicksilver was for the best. And it was literally the best scene in the whole movie.