Seems to be unobtainable, haven't heard anything about it.
Terraria Community Forums
Mihn
Techdude594
I know it can be obtained in expert mode hardcore, a guaranteed drop, but idk if it can be dropped in other difficulty settings. I hope so.
Mihn
Um, what? Drop from what? I don't seem to understand.
Techdude594
Eye of Cthulhu. It seems to be a guaranteed drop from the treasure bag. This is in reference to how 0x33 completed expert mode hardcore style, which is very hard to do!