Side-scrolling chop socky. You start out with basic characters and fight wave after wave of enemies. You defeat certain enemies and take possession of their souls, being able to use them during the game at any point in time.
Two players can team up, starting as a ninja and a guy that looks like a cowboy. You fight with swords attacking tons of enemies. When you kill them, you pick up different colored orbs for points, health, lives, or different characters. When you defeat certain people, you can use them during the game, such as a shogun, a dog, and other ninjas. The game is VERY long.