Some systems have the concept of an adversarial relationship between the game master and the players. These games typically have a series of mechanics to enforce this behavior and prevent one side from becoming too powerful and running away with the game - essentially accentuating the "game" aspect of a RPG. What mechanics of this nature are most likely to be easily adapted into another role-playing game?
To illustrate what I'm talking about, in D&D, there are guidelines for encounter creation to create balanced encounters. How could we change this to add hard game mechanics that would enforce fairness in encounter design? As an addenda, it would also be nice to see what games these mechanics come from and how easy they are to extract from the system they were built for.