Sly appeared as minor character in the episode "The Tale of the Dangerous Soup". He was portrayed by Erik Johnson.
Not very much is known about him, but it is known that is employed working at The Wild Boar Restaurant. His job at the restaurant is washing dishes and utensils. The restaurant was owned and ran by Dr. Vink. Dr. Vink became famous with his most popular dish:The Dangerous Soup. The soup was beyond delicious and became very popular. It made both the restaurant and Dr. Vink a fortune. One night he mistakenly bumped into a waitress named Jersey. This made him accidently drop a whole bin of sharp knives. Jersey would not help him pick them up, because she was afraid to touch knives.
Eventually Dr. Vink would decide when to disclose the origin of the infamous soup to him. So he would be led into a dark room, which looked like an empty freezer. Then he would be instructed to sit down. Then the wall panel would come down and a Gargoyle would came out. Dr. Vink would inform him that it knew what scared him. It turned out that Dr. Vink had somehow captured the gargoyle from a tribe of savage warriors. It used illusions to make its victims become scared. Then it would secrete a green elixir. The elixir was fear itself. Which was a powerful and tasty emotion. This green elixir was used to flavor the dangerous soup to give it delicious and powerful flavor. Also when drank, the elixir would give to the person their victims strength and powers. When Dr. Vink did this to his employees, they would become so scared, they would quit their jobs and leave.
When he was eventually exposed to the gargoyle, and what his fear was is unknown.