Cassidy Williams is a former member of the original Mystery Incorporated in Scooby-Doo! Mystery Incorporated!. She was once a lover to Mr. E because she worked for him 20 years ago. She gave her life for the gang when they were trying to escape the Kriegstaffbots. Her alter-ego is known as Angel Dynamite.
- She was voiced by Kimberly Brooks as a teenager and Vivica A. Fox as an adult.
- Brooks also voices fellow character Luna of the Hex Girls.
- Fox also voiced Lotte Lavoie in Scooby-Doo! Stage Fright.
- Cassidy Williams will meet Winnie the Pooh and his friends in Pooh's Adventures of Scooby-Doo! Mystery Incorperated!.
- Cassidy Williams will meet Ash Ketchum and his friends in Ash's Adventures of Scooby-Doo! Mystery Incorporated!.
- Cassidy Williams will meet Littlefoot and his friends in Littlefoot's Adventures of Scooby-Doo! Mystery Incorporated!.