In Stadium 2, the Doduo Game Boy Tower is unlocked for Generation I games by completing the Gym Leader Castle or clearing all of the Stadium Cups in Round 1, and the Dodrio Game Boy Tower is unlocked by completing both. To unlock the modes for the Generation II games, the same requirements must be met in Round 2.
Stadium 2's Doduo mode when used with a Generation II game changes the border to black and applies a sepia-tone effect to the game display. Stadium 2's Dodrio mode when used with a Generation II game changes the game display's tone to black-and-white. Additionally, these modes can't be used with a Generation II game until the Generation II game clears the Elite Four for the first time.