This forces me into using a specific item though. I actually want it to be an emerald. But I can't just have every emerald dropped become lightning bolts obviously. It has to be a specific emerald that you buy from a custom villager trade.
I don't think you can use uuids with dropped items.
You'll need to specify the tag-types for UUIDLeast/Most, which is type 'long'. As well, the dataTags do not start within the "tag" tag like the /give and /clear commands do; it starts within the root of the entity. You'll have to follow the NBT data for item entities, in which their item data is stored within the "Item" compound. Fixed command: