Hehe, its not just a tough one I posted some less than easy to guess with screens (your character changes form throughout the game, and doesnt look like you would expect him to most of the time).
Yes it's from the sega master system, I don't think there was a game gear version so you needed an adapter.
Game gear was a master system in portable form, like the nomad was a portable megadrive/genesis. The nomad took standard megadrive/genesis carts where as the game gear had its own smaller carts and needed an adapter to play master system games.
Here's another couple of image that might be easier to guess, if no one can get it still Ill call it quits
