Grendel

Grendel, or official title Grendel, Prince of Darkness, Slayer of Puppies, Punter of Children, Evil Incarnate, Jaywalker, and 3-Time Tax Evader, was a dastardly villain and enemy of the Plane-Stryders. His schemes were quickly thwarted when he perished outside the city of Neuhausen. Although eventually real, Grendel spent much of his life as a puppet controlled by Giles Corcyra.

Description
Grendel was suspiciously exactly what one might imagine an evil skeleton wizard to be like. He had three heads, a crown, green robes of death, and a wicked staff. In his short time, Grendel sought to conquer the world, kidnap royalty, steal from children, and invent transcontinental railroad systems just so he could tie people to them. These plans were interrupted though by a premature death.

Book 3: The Legend of the Plane-Stryders
When Cypselus Corcyra was elected leader of the Medish, his brother felt starved for attention. With the help of magic items protected by the nation, and arts and crafts, Giles kidnapped himself under the guise of Grendel. This ruse persisted for around a month, as the "two" were protected by a magical tower that required specific entries.

Eventually, the Plane-Stryders reappeared in Jaed-Najar after escaping Barovia. Meeting up with the Lynxmen, they secured the secret phrase required to get into Grendel's tower: ''Klaatu barada nikto. ''The adventurers ascended the tower and rather than finding Grendel, found Giles brushing his teeth, and a puppet. They eventually came to an agreement where Giles would be saved, and the Plane-Stryders would be honored as "heroes". In the discussion, Giles knocked over a number of arbitrary potions on the wall which fell onto the puppet. The mix of them rendered Grendel, Prince of Darkness, a real entity, complete with the stereotypical aspirations and voice Giles had created for him.

Grendel quickly grabbed Giles and flew away from the tower above Neuhausen, and the Plane-Stryders gave chase. It was cool. After being pelted by arrows and missiles, and shadowy summoned kobolds,  a strike from Craxton Monet killed the villain. His body slammed into the dirt, and Giles was saved before finding a similar fate. Grendel's Eye was taken by Craxton Monet.