I was thinking about the idea of a miniature wargame featuring ninjas today, but I decided that it wouldn't be very fun. Ninjas are just too good at killing. There wouldn't be any sort of random table for wounds because if a ninja attacks someone, that someone will die. If a ninja is sneaking up on someone, the ninja will be invisible to that person.
Maybe if all of the ninjas in the game were equal in level to each other you could play a game that lasted more than a couple of seconds, but the ninjas would eventually fight to a stalemate and go their separate ways after exchanging respectful remarks.
If you played with ninjas of different skill levels against each other, the lower-level ninjas would all die. They might see a flicker of movement as the higher-skilled ninja began his attack from the shadows, but that would be all they saw before they were decapitated in various painful, yet silent, ways. You could argue that a large group of ninjas could take out one high-level ninja, but we've all seen the movies in which a single skilled martial artist beats up 40,000 lesser fighters without even breaking a sweat.