Player versus player
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Player(s) versus player(s), or PvP, is a type of multiplayer interactive conflict within a game between two or more live participants. This is in contrast to games where players compete against computer controlled opponents, which is correspondingly referred to as player versus environment (PvE). The terms are most often used in games where both activities exist, particularly MMORPGs, MUDs, and other role-playing video games.
PvP can be broadly used to describe any game, or aspect of a game, where players compete against each other. In computer role-playing games, PvP is sometimes called player killing or PKing.
PvP combat in CRPGs has its roots in various MUDs like Gemstone II. However, while the ability to kill another player existed in many MUDs, it was usually frowned upon because of general strict adherences and heavy influences from role-playing games like Dungeons & Dragons. The term PvP originated in text based MUDs played on bulletin board systems like MajorMUD and Usurper. These games had open worlds where any player could attack any other player as long as they were not at a safe spot in town like the Bank. Player versus player was coined sometime in the late 1980s to refer to the combat between players that resulted in the loser being penalized in some way.
The first graphical MMORPG was Neverwinter Nights, which began development in 1989 and ran on AOL 1991-1997, and which included PvP. PvP was initially limited to magical attacks in the game. Later modifications expanded its use to limited areas so that players who wished to avoid it could do so. Much of the PvP activity was coordinated events by the game's guilds, which were the first such organized user groups in MMORPG's.
Genocide, an LPMud founded in 1992, was a pioneer in PvP conflict as the first "pure PK" MUD, removing all non-PvP gameplay and discarding the RPG-style character development normally found in MUDs in favor of placing characters on an even footing, with only player skill providing an advantage. Extremely popular, its ideas influenced the MUD world heavily.
Other early MMORPGs, including Meridian 59 (1996), Ultima Online (1997), and Tibia (1998) also had PvP combat as a feature. In Ultima Online, the goal was to allow players to police themselves in a "frontier justice" way. This system was also implemented in Tibia, where death included significant penalty, and killing someone inflicted considerable harm to their character. In Meridian 59, the game tried to focus PvP by having different political factions for players to join. The later Eve Online (2003) refined Ultima Online's (original) approach of "PvP anywhere but in town" (where attacking another player is dangerous in and around towns due to interference from NPC "guards"). However, these games tended to be unfriendly to more casual players. With the popularity of EverQuest in 1999, primarily consisting of PvE elements (with the exception of limited PvP on one specific server), PvP became a negative for some newer/casual MMORPG players and developers looking to draw a larger crowd. In 2000, in response to complaints about malicious player-killers, Ultima Online controversially added an extra copy of the game world to each server in which non-consensual PvP was disabled.
PvP has been included in other games such as Asheron's Call in late 1999, Diablo II in 2000, Dark Age of Camelot and RuneScape in 2001, Asheron's Call 2 in 2002 and Shadowbane in 2003. While these games included PvP, they still contained large portions of prerequisite PvE, mostly to build characters.
Player killing 
Player killing, or PKing, is non-consensual PvP resulting in a character's death. Some games offer open PvP (also sometimes called world PvP), where one player can attack another without warning anywhere in the game world. A pure PK game is one where PvP conflict is the only gameplay offered. Ganking (short for gang killing) is a type of PKing in which the killer has a significant advantage over his victim, such as being part of a group, being a higher level, or attacking the victim while they are at low health.
PvP can also create additional facets in the community. In Ultima Online and Asheron's Call, a rift formed between those who enjoyed PKing, those who enjoyed hunting the PKs and those who simply did not want to fight at all. The Renaissance expansion later added a Trammel facet where PvP was not allowed, giving some out to the UO crowd that did not wish to engage in PvP at all. Asheron's Call contained a server that was completely unrestricted in player interactions where massive "PK" and "Anti (PK)" dynasties formed.
Character death in an online game usually comes with a penalty (though some games remove it from PvP combat), so habitual PKers can find themselves ostracized by the local community. In some games a character will die many times and the player must often sacrifice some experience points (XP) or in-game currency to restore that character to life. Permanent death (such that the player must create a new character) is relatively uncommon in online games, especially if PKing is permitted. An example of such a mode is Hardcore mode on the game Diablo II.
A more rare form of player killing involves inciting a monster or monsters to attack another player. The reason this is rare is because the monster is more likely to attack the one who is trying to do the killing. Often a player will have to lure the monster towards the other player and run away, so that the monster (if it is aggressive) will look for a new target, which may be the other player. This behavior is often found in otherwise purely 'PVE' games such as Realm of the Mad God.
In some MMORPGs[specify] PvP comes with extra penalties such as the player killer will not be able to form/join a group (party), receive help from other players and may have an increased loss of experience on death. Usually a player's name who has initiated a PvP recently will be in a bright color. Arguably the most severe penalty came on Asheron's Call where a killed player incurred a 5% loss in all stats and abilities per death, stacking up to 40%. This, combined with probably being naked from item loss, was very difficult to come back from.
Some MMORPGs[specify] set a certain level requirement to engage in PvP combat in order for new players to enjoy, experience and explore the game before actually getting PK'ed by other players. Other MMORPGs, such as Anarchy Online, only allow a player to PvP with another if they are within a certain level range of each other, to prevent "ganking" (see above).
Anti Player Killing 
Anti-PKing, also known as Player Killer Killing, PK Killing, or PKK, is a form of in-game player justice. Often motivated by an overpopulation of in-game player killers, vigilante Anti-PKs hunt Player Killers and Player Griefers with vengeance.
Dueling is both consensual and competitive. Dueling ladders and leagues setup by fans are common for most MMORPGs that have PvP. Dark Age of Camelot was the first graphical MMORPG to debut a formal dueling system ingame (Ballista); other MMORPGs such as City of Heroes, Anarchy Online, World of Warcraft, Guild Wars, Lineage 2, Wurm Online, and RuneScape feature PvP as competitive, consensual dueling in a group setting.
Through various means, "flags" can be turned on or off, allowing PvP combat with other people who have also turned on their flag. In Everquest, there is no way to turn the flag off once it has been turned on. In Star Wars Galaxies, the flag may be turned off by interacting with faction specific NPCs located throughout the game or by typing an ingame command (/pvp). In World of Warcraft, flagging is selectable or can be activated by attacking certain flagged players until a cool-off period ends, though this can be exploited by griefers via corpse camping. Some games have a bounty system where players that kill or heal other players open themselves up to being killed in return. This is sometimes called the "revenge flag". Use of this 'bounty' system is not standardized among MMORPGs, and there are debates raging about how to 'police' the system to avoid abuse.
Sometimes the PvP flag gets automatically 'ON' on any player who initiates a PK. Other players who attacks a player who has the PvP flag on will NOT get their PvP flag 'ON'.
RvR (realm versus realm) combat 
In 2001, Mythic Entertainment introduced a new team-based form of PvP combat with the release of Dark Age of Camelot. In RvR, players of each realm team up to fight against players from the opposing realms in team-based combat. This can include normal skirmishes between rival groups that is common in other PvP systems, but also consists of objective-based battles such as taking and holding keeps or capturing enemy relics.
This was a new concept to graphical MMORPGs, but was first introduced in the game that preceded DAoC, Darkness Falls: The Crusade, which has since been shut down in favor of building on DAoC. Other MMORPG games now also feature this type of gameplay.
PvP in tabletop roleplaying games 
Tabletop roleplaying games have also often featured PvP action. These are usually considered a reasonable part of play so long as the fight is based on "in-character" reasons. Games are often written so player characters will not be unbalanced, ensuring that the players are genuinely scared of the other players, even when they would normally kill most non-player characters easily.
This approach to PvP in tabletop games in not universal. For example, in the highly satirical Paranoia, lethal PvP conflict is a core game element, considered normal and heavily encouraged by the rules and support materials.
See also 
- Bartle, Richard (2003). Designing Virtual Worlds. New Riders. p. 407. ISBN 0-13-101816-7. "Player(s) Versus Player(s) (PvP). Players are opposed by other players. In a combat situation, this means PCs can fight each other."
- Bartle, Richard (2003). Designing Virtual Worlds. New Riders. p. 407. ISBN 0-13-101816-7. "PvP and GvG both assume PvE."
- Reese, George (1996-03-11). "LPMud Timeline". Retrieved 2010-04-14. "January 1992 ¶ _Genocide_ starts as the first MUD dedicated totally to inter-player conflict, which is a fancy way of saying that its theme is creatively player-killing."
- Towers, J. Tarin; Badertscher, Ken; Cunningham, Wayne; Buskirk, Laura (1996). Yahoo! Wild Web Rides. IDG Books Worldwide Inc. p. 149. ISBN 0-7645-7003-X. "Genocide is a breakneck-paced, brutal MUD that has none of the mobs or quests you might be used to. It's a bloody world of kill-or-be-killed where you battle your fellow players in a savage race to the finish. [...] The only advantage the veterans have is experience and the knowledge of where to find the good stuff fast."
- Shah, Rawn; Romine, James (1995). Playing MUDs on the Internet. John Wiley & Sons, Inc. pp. 98–99. ISBN 0-471-11633-5. "Some Muds are completely dependant on player-killing, and have wars that start every half hour or so. These Muds are becoming more common, basing a lot of their ideas on the extremely popular LPmud known as Genocide."
- Bartle, Richard (2003). Designing Virtual Worlds. New Riders. p. 518. ISBN 0-13-101816-7. "Vigilantism, defending the innocent from PKs ... The killing of PKers is known as PKKing"
- Bartle, Richard (2003). Designing Virtual Worlds. New Riders. p. 407. ISBN 0-13-101816-7. "Group versus Group (GvG). Players are members of groups that are in conflict with other groups. In a combat situation, this means PCs can fight any PCs who are members of enemy groups but not those who are members of their own (or a neutral) group.63 [...] 63This is often known as Realm versus Realm (RvR), as it was popularized under this name in Dark Age of Camelot."
- Bartle, Richard (2003). Designing Virtual Worlds. New Riders. p. 411. ISBN 0-13-101816-7. "The term RvR comes from Dark Age of Camelot, but it's not the only virtual world to use this approach; indeed, it's not the only big, graphical world to do so. Anarchy Online has characters divided into three groups, with people meeting in PvP areas for combat. Lineage has clan-like groups called bloodpledges, which can conquer castles from one another in (scheduled) sieges; success here has material results, in that owners of castles get tax income they can invest in preparing for the next siege."