@Pharan > indeed, this seems much cleaner. Thanks a lot.
I'm still having trouble with it though. Here's my process :
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I have this character that is usually sporting a shotgun in most animations. For one special animation, I need him to NOT have the shotgun. Following your advice, I've created two attachments : the usual gun skin attachment, and an empty one (I've also tried having a skin attachment on the empty slot, but this doesn't change a thing).
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Then I switch to Animate, select the animation where I don't want the shotgun to appear, click on the visibility dot, the key turns yellow, I click on it, it adds a key in the timeline. Other animations are unchanged, this one looks great, all is well.
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I export my data, import them into Unity, and if I select the skeleton data and preview this particular animation, again, everything's great, the shotgun is hidden. The other animations are fine too.
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Now if I bake all the skins, and play that animation, the shotgun's still visible, and it shouldn't be.
Am I doing something wrong here ?