|Real Name||Theresa Rourke Cassidy|
|Relatives||Sean Cassidy (father)|
|Occupation||Xavier Institute student|
|First appearance||X2: X-Men United|
|Last appearance||X-Men: The Last Stand|
|Portrayed by||Shauna Kain|
Theresa Cassidy is a mutant who can emit a high-pitch sonic scream. She is a student at Xavier's School for Gifted Youngsters.
During William Stryker's attack on the mansion, her scream alerted the rest of the school that they were under attack. She was captured, but was rescued by Colossus.
Powers and AbilitiesEdit
Sonic Scream: She can scream very loudly, and at a high-pitch.