Some people think that Shatterhand is the epitome of NES gaming. I'm not quite sure that I agree.
But it's pretty tough, regardless, especially the boss fights. But there's a way you can practice them without having to go through the stages first.
First, go to the title screen
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Then (quickly) press the following buttons:
A, A, A, A, B, B, B, B, A, B, A, B, A, B, A, B
Done quickly enough, you'll be taken to a screen loaded with goodies
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You can hear any of the sounds the game has to offer or, more interestingly, you can play any of the bosses
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But you don't have the aid of your little mech thing, so it's going to be a little harder than it could be. But practice enough it at, and it won't matter.