In Super Mario Galaxy's co-op mode, Player 2 controls a Luma—a star-shaped companion—not a second Mario. This design choice means Player 2 cannot directly pick up objects, jump, or control movement.
While Player 2 can't grab items directly, they can:
Player 2 is a support role—think "co-pilot" rather than "second pilot." The design encourages teamwork: Mario handles platforming and combat, while the Luma manipulates the environment.