All he would need to do would be to take a dose of It’s not Xmas until Hans Gruber falls from Nakatomi Plaza shirt and he would be lucky enough to deal with Hans Gruber and his whole squad of mercenaries. Hans Gruber has access to automatic weapons and explosives. Severus Snape has access to magic. Severus Snape is extremely accomplished at making potions. He was even able to improve on recipes and techniques. They could have drilled the safe open in the same amount of time without risking detection from the outside. They could have simply driven away after looting the safe as no one would have known that the crime had been committed yet.
Pretty-much any performance by Alan is memorable, really, but those are good ones to start with It’s not Xmas until Hans Gruber falls from Nakatomi Plaza shirt. As a result, Gruber likely would have broken close to every bone in his body, suffered fatal trauma to his vital organs, and stand close to a 100% chance of dying instantly. Assuming 10 feet per floor plus a high plaza level, and an unobstructed fall to the ground, let’s put his total drop at roughly 350 feet. And let’s say Gruber was six feet tall and weighed 150 lbs. I maintain though, that there is no way someone, as experienced with handguns as Hans is, would have not to know that the arm was unloaded.