Gibdo Bone is a material found in Tears of the Kingdom.
Tears of the Kingdom
"A creepy bone with multiple sharp tips. Attach it to a weapon to greatly increase its attack power. It tends to break easily due to its odd shape."
Gibdo Bones can be obtained by defeating Gibdo or Moth Gibdos, which are common under the Sand Shroud in the Gerudo Desert, and can be found in the Gerudo Desert Depths - such as at the Gerudo Underground Cemetery - even after the Sand Shroud is dispelled on the surface. It appears to be the lower torso of a Gibdo.
While it can be fused to weapons with a Fuse Attack Power of 40, it has very low durability and will be destroyed after a single hit, even while mounting a Lynel (which normally does not consume durability). It can also be fused to arrows, and at +40 per arrow (including on each multiple arrow from multi-shot bows), it more than doubles the damage from most bows and is the most powerful fuse material for bows if Bone Attack Up is in effect. At a Great Fairy Fountain, Gibdo Bone is required to upgrade the Radiant Mask, Radiant Shirt and Radiant Tights to ★★★ level (10 per piece, 30 per full Radiant Set), and the Sand Boots to ★★ level (20 per pair of boots).