Young Avengers #6 First Cassie Lang as Stature (2005)

The 6-part SIDEKICKS story arc comes to a shattering conclusion when the Young Avengers lose one of their founding members, a new member arrives on the scene, and the entire team undergoes a radical transformation. It's a surprising new direction for the Young Avengers as they battle Kang, the Avengers, and each other to ensure the team's survival.