The boss on Solar known as Vulcain, alternatively known as サンガー (Sangā) or Sanger in the Japanese version of Star Fox 64, was originally intended to be the boss for Sector X.

A developer story on the Japanese website for Star Fox 64 reveals Sector X was originally meant to be the "Andross Army Biological Weapon Development Factory", and Fox and his crew were supposed to have engaged with a transport fleet heading for the factory, where they would sneak past the security defenses and enter the interior of the factory, only to find it in a state of disarray due to an accident during an experiment with robots and out-of-control bioweapons attacking all over. They would eventually come across an enemy transport ship attempting to escape only for it to be suddenly destroyed from the inside, revealing Vulcain as the stage's boss.

In the final game, Spyborg (HVC-09 in the Japanese version) is the boss of Sector X, and Vulcain was relocated to planet Solar. Vulcain's beta textures from its tenure as the Sector X boss was recently discovered within files pertaining to Star Fox 64 in the Nintendo Gigaleak.