they can deal and cause different side effects (such as knocking people to the ground with a hammer, causing bleeding wounds that deal additional damage over time with a sword, or striking multiple foes with an axe). Most skills have a governing attribute that determines its power and effect. These attributes are assigned using a number of attribute points similar to the point buy ability score generation system in Dungeons & Dragons. Guild Wars skill system is often compared to collectible card games such as Magic: The Gathering because of the way the different skills interact. While in a town or staging area, a character's skill and attribute selection can be freely modified to construct a "build". Once in a combat zone (such as an explorable area or a PvP arena), the build becomes immutable until the character exits the combat zone and returns to a staging area. Players generally either choose a specific build for a given area or role, or use builds that synergize with the builds of other characters in the party. A player's ability to help the party is based on the way a player's "build" works. If the skills combine well, such as a hex spell that makes an enemy attack faster and then another one that makes him miss 75% of the time and take damage for each miss, then the build will work effectively. In PvE, monsters that are slain will generate gold and loot which can be traded or sold to players or NPCs. Unique or rare weapon designs are often found from defeating powerful monsters, or by opening treasure chests. In PvP, reputation in the form of "faction" is gained based on how well a player performs. "Balthazar faction" is gained by the number of wins that you and your team achieve, and for each unique kill. Most PvP in Guild Wars is fast-paced, while the transition period between games may take longer. Co-operative gameplay Player versus Environment (PvE) missions of Guild Wars use several standard tropes of the MMORPG genre. Players explore the game-world, kill monsters, perform quests and complete missions to earn rewards and advance the story. Rewards include experience points, skill points, skills, gold, faction, reputation and items for the player character. Some of these rewards not only advance the particular character being played at the time, but also unlock features of the game account-wide. In each campaign