I spent countless nights fixing Unity's FBX Exporter. The code sucks, the exporter sucks.
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With my version you can actually export skinned meshes properly with animations etc.
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It's been really long since I made it so honestly don't remember exactly what it helped with but it was bones and skinned mesh renderer exporting to FBX.
## Pro Tip
FBX is the most supported file type by the Exporter, even Unity's.