The first law of ninjadynamics, an expression of the principle of conservation of ninjutsu, states that martial arts skill may only be transferred from one fighter to another. It cannot be created or destroyed.
Thus in a martial arts fight, the total amount of skill available is a constant. This statement is known as the Inverse Ninja Law or The Shinobi Law of Numbers.
Additionally, ninjas can obtain greater power by destroying other ninjas. A ninja usually reaches its peak skill when it defeats its former master.
Although the cyborg had slaughtered most of the attacking ninja army, the law of Conservation of Ninjutsu meant that the last few were very powerful and soon reduced it to a sparking heap of metal.The Inverse Ninja Law
According to the principle of conservation of ninjutsu, the threat posed by any given ninja (or other hand-to-hand combat expert) in any marital arts fight is inversely proportional to the total number of ninjas involved in the fight. This phenomenon is known as the Inverse Ninja Law or The Shinobi Law of Numbers.
Where: T=Threat; N=number of ninjas.
In real terms, it means that a lone ninja is an unstoppable force that can kill an infinite number of (for example) Stormtroopers before they become aware of his/her presence. On the other hand, ninjas in a large group are ineffective and can be slaughtered by a single well-armed hero. As the ninjas are killed off, the number of active ninjas in the fight reduces and the threat posed by each individual increases.
It is important to note that when a ninja dies, not all of their skill becomes available to the other fighters, some is always rejected into the surrounding environment as waste ninjutsu, meaning that the last ninja standing never reaches full power. Hence the net useful threat of a group of ninjas will always be less than that of a single ninja, and in a ninja-vs-ninjas confrontation, the lone ninja will always win.
The good ninja was fighting over a hundred highly-trained evil ninjas, but the Inverse Ninja Law meant that he was barely scratched as their bodies piled up around him.The Ninja's Handicap Corollary
The Ninja's handicap corollary is derived from the Inverse Ninja Law and states that if one average ninja possesses T=1/N of the total skill in a fight, then a 'completeness factor' C can be included to represent the 'completeness' of a fighter. A small reduction in completeness can mean a large increase in threat.
Where: T=Threat; N=Number of ninjas; C=Individual 'completeness factor'.
A completeness factor of C=1 represents one average ninja.
Underweight ninjas have a slightly reduced C-factor, whereas fat ninjas are not very useful in a fight because of their increased C-factor. Therefore the best ninjas often tend to be skinny little girls.
A ninja with a missing body part, scar or any other disfigurement must have a C-factor of less than one. Hence when fighting alone, a crippled ninja can pose a threat of greater than unity and defeat an otherwise healthy ninja. This can even happen during a single fight - if a ninja loses an arm or a cyborg's face is blown off and they are not quickly finished off, they can soon become very dangerous indeed.
A fighter's C-factor can be reduced by a number of other surprising means. Some examples are included below.
Because of the Ninja's Handicap Corollary, Altair in Assassin's Creed has a greater than normal ability to murder people silently due to his missing finger.
Pirates, although the antithesis of ninjas, are subject to the same fundamental laws. Hence, pirates with peg-legs, hook-hands, eyepatches, or to a lesser extent, missing teeth, have reduced C-values and are more dangerous in combat than uninjured pirates.
In Serenity, River Tam is not only a waif but also clearly not all there. Hence her C-factor is much less than one and she is able to comprehensively destroy large groups of armed opponents and/or zombies without breaking a sweat.
Both Jackie Chan in The Forbidden Kingdom and Captain Jack Sparrow are permanently legless (on baijiu and rum respectively) and hence have a surprising advantage in close combat due to their low completeness factor.