Family Feuds
If a character (run by the referee or another player) is dealt a critical hit, loses an eye as a result of another character’s actions, or feels especially betrayed by such other character, they may choose Revenge. A character choosing Revenge increases their critical hit range by 1 (e.g., crit on a natural 19 or 20 instead of just on a 20) (or whatever similar benefit makes critical hits more likely in your system) against the character who wronged them for the current combat (or imminent combat, if combat hasn’t started yet). The character targeted by Revenge may also choose Revenge, in which case they also get the increase to their critical hit range against the initial revenger. If either character dies as a result of the Revenge, a Feud begins.
During a Feud, the referee will keep track of all characters who have died as a result of the Feud. The Feud draws in not only the initial reveneger and the retaliating revenger but also both of their families. Any member of the family that has suffered the most deaths as a result of the Feud (including the initial Revenge) shall increase their critical hit range against any member of the other family in the Feud, whether or not they have ever actively participated in the Feud, by a number equal to the disparity of family members lost (e.g., if the Hatfields have 5 dead relatives and the McCoys have 1, the Hatfields increase their critical hit range from 20 to 16-20). If both families have lost an equal number of family members, any member of either family increases their critical hit range by 1 when attacking any member of the rival family until someone else dies as a result of the Feud. A Feud cannot truly end unless one or both families have been eliminated in their entirety. A Feud may be dormant, waiting for some provocation to start back, but it is not done.
I envision three possibilities with this set of rules: (1) if the player-characters kill an NPC in a bout of Revenge, it gives the referee an opportunity to send the deceased NPC’s relatives against the party, looking to settle the score; (2) if an NPC kills a player-character in Revenge, it gives a good motive for the player to roll up a new character who is a relative of the deceased character. Now, they have a dramatic backstory and a motive for taking up the fallen character’s cause; and (3) the most exciting option is the players using this in a metagamey way to give themselves a leg up against a powerful foe. I could envision a group of scrupleless murderhobos deciding to attack and kill their enemy’s relative and/or provoking the enemy into killing some family member they wouldn’t be too torn up to lose, then use that as an extra edge when they eventually confront the enemy. The players could also all decide to be a family. Now, if you mess with one of them, you mess with all of them.
