Problem Collecting Malachai's Organs

I am currently in the Harvest trying to access the Black Core. I have killed all three mini bosses but the third did not give an organ. So the boss will not spawn again, but I cannot get into the Black Core because I have no third organ. I need help.

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rfialkiewicz wrote:

I cannot get into the Black Core because I have no third organ.

Had you tried?

The game requires that you kill each of the three bosses before accessing Malachai's arena, however the organs only drop a single time as they are part of a quest. They'll never drop for that character again, and he or she will never need them - though they will need the other bosses to be dead.