Object Id???????

If you used an actual object type number instead of ext="true", First make sure that the number isn't already used, then you have to put that item's code into dat1. After that, you'll get that art jumbled sprite that you were talking about, so you'll have to decompile your client with JPEX, open the binaryData folder, and export the 30th file down, which have "EquipCXML" somewhere within it's filename. Now, you'll have to open the EquipCXML file with NotePad++, and go to the bottom of it. Remember when you pasted your item code into dat1 in the server earlier? Now you'll have to also paste that code into the EquipCXML file, save it, and then in JPEX right click that file and click "replace", and then replace the file inside the client with the file you had exported and edited.

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If my explanation about the client part was a bit confusing for you to understand, there are other tutorials on how to edit XML's within the client. Those tutorials will say you can use the 1st bin inside the client, which is named something like "GhostShipCXML" but using EquipCXML for custom items is preferred IMO because it keeps things much more organized.