Legacy of the Distant Lords
The fatigue system is designed to prevent drawn-out battles. As I have noticed with some battles in D&D 4th edition, a fight with an elite or solo monster can drag on and become boring. This system helps to conclude fights once they reach this point. The concept presented here can be used for any other table-top rpg, just keep in mind the goal is to make fights concise, not easy mode.
Anyone who has been in a fight or participated in a high intensity sport can tell you, the strain of acting at peak performance can quickly wear your body out. The same is true for an adventuring group fighting monsters. This system represents the bodily effects of sustained fighting, including: lactic acid buildup, loss of adrenalin, confusion, and many other factors. The number represents how many turns a creature can act at peak performance before their reflexes become slugish and their defenses weaken. The first turn after the limit is reached and every turn afterwords, the creature looses one point of AC. By using a second-wind as a full-round action, the creature can refresh this counter (new count begins on their next turn).
A fight consists of three creatures. One with fatigue 2, 3, and 4 respectivley. Starting on round 3, the creature with Fatigue 2 takes a -1 penalty to its AC. On round 4, the fatigue 2 creature is at a -2, and the fatigue 3 creature is at -1 before it takes its second-wind. On round 5, fatigue 2 is at -3, fatigue 3 is at -0, and fatigue 4 is at -1. Fatigue 3 will not recieve an AC penalty until the beginning of round 8 (round 5 becoming its new first fatigue round).
*Surprise rounds do not count towards fatigue.