The problem is that the bubble and fire object you're talking about is a .particle object, not a .mesh like all the items are. As far as I know you can't use particles as items, they're not an actual 3D object like mesh files but script.
How you said "animated" gave me a bit of an idea, however. Using a series of images and using a certain script in the .material file might work. I must experiment with it though before I'm certain.
I'll see what I can do but I can't guarantee anything :3