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OK, let's go, you need to look at the files I gave as an example, maybe this codex item that you mentioned is there in the middle, as this item would not be an item that drops from mobs naturally, so basically it is a drop addition made, in this example that I passed the server edits, such as drop and spawn mobs and NPC
View attachment 254888
You can also look directly in the XML where the mob data is located, to see if there is something linked to them, which I think is kind of difficult to have something but it doesn't cost you anything to look to see if there is a config directly in it.