been working to unlock my bolt caster exotic sword and my fire team has gone three times with me throught the 300 sunless cell quest and we kill the arc knight just before alak-hul dies and well within the 30 seconds yet the quest keeps refusing to give me credit for killing alak-hul.
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Killfire and void weaken arc to a sliver and then weaken boss. Once boss is low enough u kill the arc knight and kill boss and its done.