FREE ITEM UPDATE
A photo of the Holy Corpse Left Eye from Trello
By using it on Standless, you can get USHAAA Dinosaur. It doesn't really have a use other than that.
Fun Fact: When you use Cone Platinum's V attack (and some others), a small orb will be left. Some people mistake it for a Holy Corpse Left Eye, and walk around it, trying to get it. The only difference is that that this orb is pure white, rather than the slight yellow of the Holy Corpse Parts.