Currently, the witch pupil and the undead soul inject items into one loot table (the witch and skeleton horse respectively). It would be nice if we had more customization like the eyes' loot table injection. This would be useful for modpack creators like me so I can decide to make the undead soul also drop from the zombie horse as they can also spawn alongside skeleton horses from the Friends and Foes mod.

It would be convenient to allow a list for the loot injection, but you can always make a new file to inject the undead soul inside the zombie horse loot table if you want to.