User blog comment:MemoryAngel/How are Creation, Destruction and Darkness confirmed?/@comment-25374175-20151014234648

Okay, Darkness is not only seen when the Overlord consumes the three ninja with evil.

It is seen when Lloyd and Garmadon (with the Dark Lord’s presence) battle against each other in the 22nd episode.

Seeing each how Golden Power is an element and Darkness is the corrupted version of it, I think it is an element itself. Plus, if it was an ability, everyone would have access to it; similar to Magic.