Four thousand on-lookers watched as Derian Moffitt stepped on to center ice. Donned head-to-toe in a Cat-in-the-Hat costume, holding a pink broom, he laughed and joined a small pumpkin girl and 18 other costumed heroes in an epic broomball battle at a recent Giants hockey game. Up until recently, this kind of attention would have been a horrific nightmare for Derian. Since his earliest memory, Derian, now 20, has lived with crippling anxiety—sometimes so bad it left him unable to leave the house. “He has always feared what people would think of him,” says Youth Unlimited outreach worker Cassia Philipson—aka...