The Science of Superheroes - X-Men

BBC Science has an interesting article on The Science of Superheroes. I've included some of the article below, but there's much more on other superheroes like Spiderman, The Incredible Hulk, and Daredevil.

Levitation
We're all used to the idea of magnetism. Iron and steel are magnetic, and are attracted to either the north or south poles of a magnet. You can also use electromagnets to make levitating trains (called 'Maglev') that float over the rails. These are much easier to move forward than a conventional train that loses a lot of energy as friction between the rails and wheels.
The Maglev trains and rails are fitted with electromagnets that generate two opposing magnetic fields. Just as two north poles cannot be pushed together, the opposing magnetic fields keep the trains a few centimeters above the track.

Floating frogs
Most materials are 'diamagnetic', meaning that they are always repelled by either of the magnetic poles. Water is slightly diamagnetic so it's also repelled by strong magnetic fields.

Since animals are mostly water, scientists have found that if they use a strong enough magnetic field, they could levitate a live frog – and it doesn't hurt the frog at all.