Sturdy Helixhorn

Sturdy Helixhorn is a treasure.

Source
Sturdy Helixhorns can be obtained as a drop from the following creatures:
 * Duplicorn - Appendage break, 10% chance
 * Leukorn - Appendage break, 75% chance
 * Spiracorn - Appendage break, 75% chance (hunt variant only; normal enemy drops Crooked Helixhorn)

Quests
Sturdy Helixhorn is needed for the A Better Engine Blade III quest to upgrade the Engine Blade III to an Ultima Blade.