Not a very original idea, but I thought I'd throw it.
Shadows are a weird phenomenon among darkness elementals. While it is made from ambient darkness, Shadows or Shades have no physical bodies. Shades are pretty rare in the dark temples of Felarya, but very common in Sunfall Thicket. Because they lack physical bodies, nothing but energy or magic attacks are effective against them. Light is extremely reccommended to fight these. They are deceptively fast and their shadow magic are nothing to mock. They also are fond of magically inducing fears in their victims before engulfing them in their ectoplasmic bodies. One interesting thing to note is that they can immediately be banished without needing to destroy the body, but the task is more difficult to accomplish than with a natural elemental spirit.
If someone has a better idea, by all means, spill the beans. (Rhyme more or less intended)