Cassie is a character in Halloweentown High. She's a witch and one of the transfer students in the film. With the exception of her old friend Ethan Dalloway, Cassie is the only one of the transfer students to not need to disguise herself with a magical costume, only wear appropriate clothing for attending a mortal high school.
When she first meets Marnie and Dylan, the first impression given about her is that she's energetic, inquisitive, and a bit dense; she openly asked if they were humans, something that would be a dead give away that she wasn't.
Edgar Dalloway later sealed her in a Witch's glass to help instigate things by causing a disapearance. Gwen later found and freed her, allowing Cassie to join her friends in the haunted house. Once the Council decided that there was no threat to Halloweentown anymore, Cassie joined everyone at the fair for fun.