Ninja Gaiden: Dragon Sword Cheats

To unlock a harder difficulty setting than is initially available to you, beat the game once through.

Ninja Gaiden: Dragon Sword Unlockable: All Artwork

To unlock all of the in-game artwork, simply beat the game once through.

Ninja Gaiden: Dragon Sword Hint: Money Farming

There's a part of the game where you can jump into a well, leading you back to a village. There are bats in this well. Attack and kill them, grabbing what goods they drop, and then jump back out of the well. Jump back in (as the enemies have respawned below), and repeat this process for infinite funds.