Yet he is still human. Just because u can control all of the elements on the Periodic table, doesn't mean you're unbeatable. X-Man and jean can affect matter now on a molecular level. Even if he did turn into crystal, it is a proven fact that crystals have pressure points in which one can capitalize on. U say he turns into oxygen? Storm can drop the temperature to sub zero and freeze his molecules or Jean can excite the electrons blow him up. Scartlett Witch says a spell and teleports him into a blackhole. Flash can speed up the oxygen molecules until it sets on fire. Crystal can do the same thing or command elemental lad in his oxygen form to dissipitate.