Perfect Performance

At least 4 people present (don't need to be in a group) need to perform one role each from the Taking this Show on the Road achievement during the Blight Boar concert:

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• One who avoids all Banshee Walls and stands in all the Bolts of Light, the Drummer.
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• One who avoids all Banshee Walls but misses at least 1 Bolt of Light, the Bassist.
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• One who gets hit by at least 1 Banshee Wall and stands in all the Bolts of Light, the Vocals.
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• One who gets hit by at least 1 Banshee Wall and misses 2 of the Bolts of Light, the Guitarist.
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Unlike what was said in other comments, the concert isn't over when the death metal knight is dead. The concert is over when the band disappears. After the death metal knight and the ghouls are down, continue catching the bolt of lights cast by the undead npc in the arena until the npc's are gone.

I've seen people leave before the event is completely finished. Whether or not these people were working on this achievement, I cannot say, but I suspect this is the reason a lot of people claim they didn't get the buff despite doing everything correctly until the DMK has died.

The previous person might be right. Just got this achievement.

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• I had Drummer on my previous event (didn't cancel the buff), which got replaced by Vocals this time (got hit by 1 banshee wave)
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• Another person won event this time and got Guitarist buff.
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• Third dude had Bassist buff from the previous event (didn't cancel it either). This time around he didn't win, but his previous buff got counted.
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• And supposedly, someone else got Drummer buff (personally I haven't noticed him, probably he ran out of the cave rapidly). Maybe my previous Drummer got counted together with current Vocals (not likely).
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A lot of people got hit by banshee waves, a couple died, several didn't get any buff at all.
But, every person present got the achievement, even ones that didn't won any role, neither had "number one fan" from previous attempts.