Maybe being unable to wear armor would be a little much. How about a restriction against metal armor. And not so much a restriction, but say that it interfere's with the usage of physical mana, making the classes special abilities more difficult to use.

Well, after I posted, I thought of a couple of other abilities.

And they'd actually be finger claws, not claws that pop out of the wrist

Poison claws - Chance of poisoning target when attacking
Acid spit - Spit acid at target
Glue spit - Spit glue at target, slowing or immobilizing it.
Electric Palm - Focus body's electrical energy into a punch.
Far Punch - Punch through a dimensional vortex to an unprotected spot on target. Can be delivered from missle range.