Xydia Horton
From Lunar Shadow Project Wiki
Also known as Xyz, Xydia Horton is the mother of Valerie Horton, the father of whom is Ladislaw Smit. She was a human until she was transformed into a monster by Aidan Flamberge's magic.
Story
Xydia was kidnapped by the Castle Master, most likely at the same time as Valkyrie Horton. Aidan then transformed her into the monster Xyz, who was taken on as a pet by Shinica.
In-game
In Lunar Shadow, Xyz is found in the Entrance, and may be the first boss encountered. This fight can be delayed until much later, however, because the only reward for defeating her is access to the two rightmost rooms of Entrance, which can also be reached through the Servant Quarters. If fought after Grialdyn, Xyz has a second form, Xyz EX.