The Sydyru Bone is a legendary crafting material used by Blacksmight Haedrig Eamon to craft the Sydryu Crust (2-Hand Legendary Bow). The Sydyru Bone is a randon drop off the Plague Carrier (rare spawn) named Sicklefang. Create a normal-difficulty Adventure-mode game. Go to the Act I: Fields of Misery waypoint. Locate the Forsaken Grounds and talk with the Beleaguered Farmer. He starts the quest titled Carrion Farm. Kill the four Plague Nest. The last plague nest will auto-spawn Sicklefang where the plague nest was located. If no Sydyru Bone drops, keep creating new games until it happens. Took me about 20-30 attempts.