FUNDAMENTALS OF GAME DESIGN, SECOND EDITION
The Player-Killer (PK) Problem
No aspect of the design of persistent worlds has been debated more than this one simple question: Should players' avatars be allowed to kill one another? The next few sections summarize some of the issues so that you can make an informed decision for your own game.
Most designers offer persistent worlds resembling role-playing games in that players advance in skill and power through combat. It's generally more interesting if this combat occurs against another player rather than against an NPC, for several reasons. First, another player's avatar is more likely to be carrying interesting and valuable objects worth looting (if the game permits looting) than a randomly generated NPC; unlike an NPC, another player will have kept only valuable items and gotten rid of anything not worth keeping. Second, fighting another player is a social experience, which an NPC cannot offer. Finally, a player can use his human intelligence to put up a better fight; an NPC has to use AI, which is seldom as sophisticated.
The designers of Ultima Online initially permitted players to kill one another without restraint (except in towns), hoping that players would establish their own justice mechanisms within the game. Unfortunately, the world quickly began to resemble present-day Somalia: unremitting random violence, feuds, continual victimization of the weak by the strong, and petty warlords or gangs of bandits controlling areas of turf. Players engaging in this behavior became known as player - killers, or PK players. No satisfactory solution arose from the players, partly because the software did not offer any genuinely painful punishment mechanisms for them to use against offenders. (In real life, we either lock murderers away for a very long time or kill them permanently, neither of which any for-pay persistent world can afford to do.) Designers then tried a variety of different automated mechanisms for encouraging justice, but players found ways of exploiting most such mechanisms.
In the end, the developers threw up their hands and divided the world into shards (separate, independent versions of the world) with different rules for each. Some allowed player-versus-player (PvP) combat, and others did not. Approximately 80 percent of the players chose to play in non-PvP shards.
Koster offers the following summary of approaches to regulating PvP combat, whether fatal or not:
■ No automated regulation. Anyone can attack anyone, and administrators or social mechanisms (vigilante justice) deal with rogue players. Koster estimates that as much as 40 percent of the potential audience will avoid this type of game because they don't like PvP.
■ Flagging of criminals. Player killing is considered a criminal act within the game's rules: not prevented by the system, but wrong. The server automatically detects criminal behavior and flags the criminals, who become fair game for others to attack. The system can also reduce the attributes of criminals, in effect penalizing them for their behavior. This can be used for thievery and other crimes as well as murder, matching the reduction to the severity of the crime. Single-player RPGs use a version of this system too: players may behave in good or bad ways, but those who behave badly frequently suffer penalties—NPCs will not talk to them or trade with them, for example.
■ Reputation systems. This is similar to flagging, except that players decide when to report someone for criminal behavior and can choose not to do so. In practice, they almost always do, however.
■ PvP switch. Players indicate their willingness to fight other players by setting a switch (a binary attribute) in their profile, becoming either a PvP player, who can attack and be attacked, or a non-PvP player, who cannot attack or be attacked by others. You can use this switch to give temporary consent for duels and arena - based combat. Unfortunately, this mechanism creates suspension-of-disbelief problems when players use area-effect weapons such as a magic fireball spell: Three PvP players get roasted by a fireball that leaves a non-PvP player in the same vicinity untouched because he cannot be attacked.
■ Safe games; no PvP allowed. This is the least troublesome solution, but even this approach has its hazards. Players will still find ways of abusing one another— for example, by luring an unsuspecting newcomer into an area where he will be attacked by a monster. Koster estimates that this approach will cost you up to 20 percent of your potential audience, that 20 percent being those players who like PvP.
You can also divide the world into safe and dangerous geographic zones, but in practice people tend to either stay in the safe zones or play near the edges, hoping to lure a potential victim over the line without his realizing it.
