Nimbus

 was an enormous raven that Brianna Barter befriended while studying at the Vargrend Academy disguised as Lady Bellany Norwit. He appeared shortly after Brianna read a prayer to Mortaebius for an omen.

Ravens are a symbol of death, and are thus associated with Mortaebius, the god of death. Ravens in general, and Nimbus in particular, were considered omens of the god; and he was called more than once a Raven of Omen. During an exceptionally cold spell, Brianna saved Nimbus from freezing.

He became very friendly to Brianna, and served as an object of a number of spells, including
 * Gentle Beast
 * Telempathic Projection (to see through his eyes)
 * Life Vision (to let him see and fly in the dark)

Brianna called him Cindus, to avoid recognition of the unusually large raven that was associated with Bellany Norwit.