The Blackened Femur stands as one of the pivotal Malignant Body Parts, Like Trembling Hand, integral for calling forth the Echo of Varshan within the ominous confines of the Malignant Burrow. This particular locale is situated in The Writhing Mire, adjacent to the mysterious Tree of Whispers, nestled in the heart of the Hawezar region. 

Getting Blackened Femur

• Tree of Whispers Cache: The primary method of obtaining a Blackened Femur is by opening a cache from the Tree of Whispers. To maximize your chances, head to a Blood Harvest zone during The Season of Blood and farm Whispers. Open any of the caches you find, as they might contain the elusive Blackened Femur.
• Rare Enemies: Rare enemies found in Blood Harvest zones that spawn from a puddle of blood have a chance to drop Blackened Femurs. Hunt down these enemies and increase your odds of acquiring the required item.
• Refining Other Parts: An alternative, albeit less convenient method, is to refine other Malignant Body Parts at an Alchemist. This will yield a Malignant Body Cache, which might contain a Blackened Femur. However, many players consider this wasteful since it consumes one of the three essential parts.

Blackened Femur Using

Once you have obtained a Blackened Femur, you can combine it with the other two required items to summon the Echo of Varshan. To do this, visit the Tree of Whispers and enter the Malignant Burrow, where you'll find the Malignant Altar. Having all three required items will enable you to summon the Echo of Varshan, a formidable opponent that can yield valuable loot, including Legendary and Unique items.

Verdict

It's important to note that the Echo of Varshan can be summoned multiple times as long as you reset the dungeon and possess the necessary Malignant Body Parts. However, refining materials to obtain Malignant Body Caches might not be the best strategy, as it consumes not only an item required for summoning but also other rare ingredients. Before summoning the Echo of Varshan, it's advisable to gear up and prepare for a challenging battle to ensure that the summoning items are put to good use.