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Highlord Darion Mograine wants you to infuse Shadow's Edge with Unholy power and slay Professor Putricide. This quest may only be completed in 25 person difficulty of Icecrown Citadel. The entirety of this quest happens in Icecrown Citadel.
Before your weapon can reach its full potential it must be endowed with its signature powers. First among them is unholiness. You must seek out and defeat the one called Professor Putricide, but his death is not your only goal. You must use his resources against him. Find a way to absorb his mutated slime. Use the foul substance to infuse your weapon with the power of the unholy. Only when this has been done shall I reveal your next task.
Here you can buy Unholy infusion quest boost for EU or US Servers.
Also you'll get guide for completing Unholy infusion quest
You“ll be able to complete one of the quests for Legendary Shadowmourne quests chain
Completing the quest "Unholy infusion"
Knowledge how to do it
350 reputation with the Ashen Verdict