While the main game in ''GuildWars'' cannot be made unwinnable, some missions and quests are made Unwinnable by bugs or accidents:
* A mission relatively early into Prophecies can be made unwinnable if the wrong boss spawns at one spot. If the Monk boss spawns right next to a group of mobs, then you'd best get ready for a wipe...you can't kill the monk or even the other monk mob because they just won't die unless you happen to have been getting run through!
* Several times, it's possible to aggro everything in the instance. Warriors/Monks got a bad reputation for this.
* A bug in Vizunah Square would cause Mhenlo and Togo to stop dead in their tracks. When they couldn't move, you can't complete the mission.
** Specifically, the [=NPCs=] are given a set path to follow. Random chests are added as you go, and cannot be walked through, you must go around. The [=NPCs=] are unable to divert from their scripted path the half step needed to walk around the chests and become stuck, thus unable to fulfill their role in the mission script.
** As an added bonus to Vizunah Square. Before you could command henchmen, they would follow you unquestioningly. When Factions came out, on the condition that the Canthan group would only be comprised of eight henchmen and no players, they would attempt to reach the Tyrian group. This results in them leaving Master Togo (who needs to be alive) completely defenseless, so he dies before you are even able to reach him. They fixed it a few months later.
* Another bug would make the final mission in Nightfall unwinnable. You have to kill Monoliths to be able to damage the final boss' health; a bug would make them not stop spawning, leading to an eventual party wipe.
* Treasure chests randomly spawn at widely scattered locations all over the game. If you're really unlucky, one will spawn right in the preprogrammed path of an important NPC, bringing them to a halt and making whatever quest you're doing with them impossible to complete without restarting.
* In one of the ''Eye of the North'' missions, "G.O.L.E.M.", you're expected to protect a golem factory from invading Destroyers and then use the newly manufactured golems to help you kill the remaining Destroyers. If your party is so efficient that you manage to kill all the Destroyers, including the end bosses, before any of the golems are completed, then the mission becomes unwinnable. (This can be avoided by staying well clear of the boss spawn points until at least one golem is ready.)
* An early mission in Nightfall can be made unwinnable by a glitch if you desperately need the bonus. One of the required enemies can spawn behind an unopenable door. What's worse is seeing his little red dot on the map and knowing you can't get to him. Luckily, you hit the bug pretty fast, so the required restart isn't too painful.
* Sometimes Mineral Springs is impossible to vanquish and must be reset to try again. Vanquishing involves defeating every foe on the map in hard mode, and one group of Mineral Springs enemies can spawn outside the zone. As in that early mission, you can see them, but you cannot get to them.
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