Weird shadows and trasparency on custom Build Mode Items.

Try not to use decimate if you can help it; it is death to your topology. Or just use it for the lowest LOD. The lowest LOD doesn't matter much since it's only displayed when you're very, very far away from your object so you don't see the errors. Instead, at least for LOD 1, dissolve edges. It helps to turn your tris to quads first. Press T to open the side panel, select your mesh, edit mode, press A, Alt + J, put a checkmark next to compare UVs. Sometimes, turning tris to quads messes up the UV map, and compare UVs fixes that. Press T to close the panel.



Enter edge select and hold Alt and select an edge loop, X > dissolve edges. Or hold shift + alt to select multiple edge loops.

Speaking of your uv_0, you've got one island that's not on the map at all and one that is located over a transparent area of your texture. Put the island that's off the map on top of the one that's over the transparent area and select both with B then S to scale them down. Put them somewhere on the map. They both are part of the an eye so just stick them somewhere where there's a dark color.



Face select, select one face on each helmet. Press Ctrl + L and all connected faces will be automatically selected. Press H to hide what's selected. Delete the faces that are inside the helmet (X > faces). As a rule, you should always delete geometry that won't be seen. Alt + H to unhide.

Don't clone a sink unless you want your mesh to behave like a sink. If it's just decor clone a decor item. Clone a statue if it's a floor item. Clone the stack of books if it's a tabletop item (you can use something other than the stack of books; it's just what I always choose).

Re: the CAS item not lighting up when you mouse over it. Prolly, it's because of the uv_1 and/or the vertex paint. The uv_1 and vertex paint are both needed for your item to respond to the CAS sliders. I'd have to see the file to tell you for sure if the uv_1 or vertex paint is messed up.

As for shadows, take a look at this thread.

The reason I wrote what I did about selecting the helmets is so that you can hide those faces and get access to the heads inside and delete those parts. You can select faces via the materials? I didn't know that. How is that done, please?

As for vertex paint, the general rule is to mimic what EA does. The uv_1 is for the CAS sliders and vertex paint is a way to...refine, I guess you could say, the uv_1. It all works off of a deformation map in the game that's made up of different colors. The colors represent numbers. They represent values. I can't explain it more than that as it gets into coding technicalities that I'm not very knowledgeable about. 

I DID NOT KNOW YOU COULD DO THIS. Coolest thing ever. I'm working on two tutorials that are both conversions and this is the first time I've done anything involving a conversion. Selecting a mesh part via a material? Fantastic. I love it when I learn little tricks like that. Thank you so much for sharing that!