Demons easily outstrip any others in their ability to store and use magica. They in turn may be the most vulnerable to magica, but since they can use magic to defend themselves this weakness is easily overcome.

Shielding, energy blasts, flight, and bodily enhancements are common to almost every demon.

As they become more advanced in their usage they also learn to cast advanced spells. These can be vastly varied, and there is no way to know the full extent of a demon's abilities before confronting them.

The more powerful demons do seem to have a unique ability which is a MANIFESTATION of themselves, directly through their stored magical energy. This creates an immensely powerful aura construct. This acts as both a near perfect weapon AND shield. This is a wasteful use of magica, and for anyone besides a high level demon would be nearly impossible. 

Still, when backed into a corner high level demons have been able to use this ability to devastating effect, even against large numbers of opponents.

DO NOT ATTEMPT TO DO THIS YOURSELF. DO. NOT.

-A beginners guide to Magic and its practical uses