Ninja Gaiden: Shadow (Ninja Ryukenden GB Matenro Kessen in Japan, literally Legend of the Ninja Dragon Sword GB: Skyscraper Showdown, and Shadow Warriors in PAL regions) is an action platformer developed and published by Tecmo (with development assistance from Natsume). The game was released in 1991 in North America on the Game Boy. The game stars Ryu Hayabusa and is part of the Ninja Gaiden franchise.
The game is commonly believed to be a licensed edit of the Natsume Nintendo Entertainment System game Shadow of the Ninja. The two games share many similarities and have many differences, so credible evidence could be amassed to support either side.
The game follows Ryu Hayabusa in his battle against Emperor Garuda (his name is Emperor Gulf in the PAL version of the game). Emperor Garuda has taken over the majority of the western world. Ryu battles many of Emperor Garuda's minions, such as a cyborg named Spider, a kick-boxer named Gregory, the Colonel Allen (who could be a traitor to earth), and a wind god.