to be fair, the physics is mostly sound, mostly. MRI magnet for instance, are capable of actually pull something like a chair into it with serious force. So consider that the knife are throw in numbers and are much smaller and lighter, it is possible for the pulling power to actually large enough to cause damage. especially with how many knives he toss at once. The sheer numbers of knives cover the shortfall of accuracy and control.
Now here is the problem, the magnetic field shouldn't be that big. As in, actual MRI magnet probably capable of pulling light stuff from 4-5 meter away, but I doubt what they managed in middle age has that level of power. To understand it more easily, if knife is pulling at 3m get to 1m, the pulling power is exponentially increase, as in the closer the item is to the magnet, the bigger the force is. So if the Priest instead of throwing the knife on to the air, but throw it at our devil, then it's fairly accurate, since the initial vector and force cover for the weak pulling from the distance. But he toss all of them on air so this is actually a bit of a stretch, since I doubt whatever they can cook up in medieval is that powerful, or even if they somehow could, where the hell do they get the energy to power something like that, seriously, don't make me think that there is a group of zealots who is sitting and pedaling wooden bike to power it. The arena seem cover at least 8-10 meters. That's really hard unless the priest stood at the very center.
The actual issues in my eyes though. is the coordinations of the magnetic team is way too good. As in. To make the knife fly in curves. The magnetic 2 that is right next to magnetic 1 have to turn on at the timing where magnetic 1 turn off his magnets, since the knives is closer to magnet 1. But magnet 1 can't turn off too soon since the knife risk losing momentum and create a dip or even fall on the ground in that room. A seamless curve like that is just some godly teamwork. And not to mentions that the magnet operator operate only on eyehole. Seriously, if our devil has this team he is unstoppable.
EDIT: checked the books again, I think someone already mentioned in this thread, But electric magnet of this caliber are loud, so while it might be that there is a lot of noise in the arena, but I do agree that people should notice the noise of an electromagnet. That is unless the magnetic team control is godly enough that they turn on and off with a timing so impeccable that the noise blend in the background, seriously those guy operating the magnet are the true MVP on the church side.
