Or devs could take control of the mobs. That would be even more fun.
Icefalcon: I don\'t think a story needs to go with it, just every once in a long while (these things would be rare) a hoard of monsters decide to assult the city.
I think a story can be incorporated behind the attacks, yet not with every specific attack so it would still be unexpected. They just need a background as to why these hordes of creatures attack the towns randomly and that should give them a blanket large enough that they can have these events and catch everyone off guard.
I remember my most memorable night playing EverQuest. I was in a zone hunting with a group from my guild when suddenly a zonewide message came up from the voice of a character (normal PC\'s can\'t do zonewides, a different kind of shout) predicting everyone\'s doom or something. Then two giant spiders with crazy names came and mowed through our group! It was obvious at this point that this was a GM event (live event). Especially when I respawned and hadn\'t lost any exp. I ran back to the zone, and was followed to my corpse by one of the two spiders. I knew I would never stand a chance, and that I wouldn\'t be penalized for dieing, so instead of fighting or running I gave it a /rude (rude gesture) over and over. In the end it took a pretty descent sized horde of really uber characters to bring the spiders down. And as it turned out I got the loot from both spiders! 99.9% of all EQ players, uber or not, have never gotten GM loot. While the loot wasn\'t really anything incredible, just the fact that I got it from a GM event is pretty special. I split the loot with my group, and gave away a wedding ring to a stranger who was getting married in game. Afterward I got to meet the GM\'s who were controlling the mobs and I thanked them profusely

I\'m not really a fan of EQ anymore, but I must say that that event was hella tight! Anyway, it\'s stories like these that you want to create good publicity about your game, and IMHO PS should definitely take advantage of it. Sorry for the long post.
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edit: I forgot that you guys probably don\'t know what a mob is

Mob is short for \"mobile object.\" It comes from MUD games back in the day. It basically means any sort of monster or NPC.
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