I am not near my desktop now but you would want to make an FX first. Then you can call to the FX spec and attach it to the item you have displayed in the world. In this case the said loot box.
You will also need a system for manipulating or choosing different FX's for different levels of loot.
imho I would do classic "Grandmas Boy" and just change the color of a single FX for different levels of loot by manipulating one of the FX's layers diffuse.