Lorr

The Lorr were a race of shapeshifting humanoids. Their homeworld was destroyed, Ballon and his family, including his niece, being scattered as refugees. Ballon died inside the Cabinet of Souls, while Dorothea Ames claimed that Ballon's niece was alive and well on Earth.

Lorr lived in the "constant flow". They believed in a place called Lorr ap Thriss, basically Lorr Hell, a place where they would become statues, unable to flow between one form and another. It was guarded by the God of the Lorr. The Lorr saw people who were unable to shapeshift as being already dead. (TV: The Metaphysical Engine, or What Quill Did)

Biology
It's little known the Lorr's true froms looks like, but it can be asumed balls made of light. (TV: The Metaphysical Engine, or What Quill Did)