Did you know, Ninja Gaiden Shadow ("Shadow Warriors" in Europe and Australia) for the Gameboy was not originally planned to be a Ninja Gaiden game? The game was actually going to be a port of the NES game "Shadow of the Ninja" developed and published by Natsume, but due to publishing issues found its way into Tecmo's hands and was reworked to be a Ninja Gaiden prequel.
In Nintendo Power vol. 28 page 67 there is a screenshot of the game where it is still named "Shadow of the Ninja" with the text describing:
Quote:Another one to look for is Shadow of the Ninja, an excellent Game Boy adaptation of the NES ninja thriller. This version includes new settings and new enemies along with the same great play control and the same cool acrobatic moves.