Magus was a female horse that belonged to Mary and Finella in 997.
Mary named the mare after the Magus because "there was something about her face." ("The Gate")
During the Battle of Rathveramoen, Brother Valmont used the Grimorum Arcanorum to bring down a rain of magical arrows. Magus was killed in the onslaught, much to Mary's sorrow. ("Phoenix")
Note: This character does not speak, therefore she does not have any lines.