Firmament/docs/Texture Pack Format.md

Custom SkyBlock Items Texture Pack Format

Items by internal id (ExtraAttributes)

Find the internal id of the item. This is usually stored in the ExtraAttributes tag (i will soon-ish add a command for finding the texture pack id specifically). Once you found it, create an item model in a resource pack like you would for a vanilla item model, but at the coordinate firmskyblock:<internalid>. So for an aspect of the end, this would be firmskyblock:models/item/aspect_of_the_end.json (or assets/firmskyblock/models/item/aspect_of_the_end.json). Then, just use a normal minecraft item model. See https://github.com/romangraef/BadSkyblockTP/blob/master/assets/firmskyblock/models/item/magma_rod.json as an example.