Ninjatown is a peaceful place populated by ninjas. But after a volcanic eruption, Ninjatown gets invaded by enemies and their leader, Mr. Demon, who is bent on destruction. It's based on characters created by toy designer, artist and former Electronic Gaming Monthly editor Shawn Smith. Smith is the artist behind the Shawnimals line of toys. Ninjatown is a spin-off of one of his Shawnimal characters, the Wee Ninja.
Ninjatown is a tower defense strategy game. When an enemy reaches a certain point on the screen, it disappears, taking 1 life from the player's 10. At the end of the level, the player is graded from A to D depending on how many lives he/she has lost. Completing the level with no lives lost will award an A, while losing 1-2 and 3-4 will result in a B and C, respectively. Losing any more lives will result in a D, and losing all lives forces the player to restart the level. Additionally, if a player has lost several times on a level, they will be given the choice to play the map on Easy Mode. If the map is successfully beaten on Easy Mode, the player will be "awarded" with an E, regardless of how many lives they had lost in the level.
Source: Wikipedia, Ninjatown , available under the CC-BY-SA License.