Just because unity does it, it doesn’t mean what they do is viable for performance across multiple platforms when you use it.
In the example you bring, for instance, you would probably get Very poor performance after stacking together 4 or 5 different animation “layers”.
While you are absolutely correct that often enough the UI is lacking, and you are even more correct in that the docs are terribly out of date, and yet again correct in essentially saying that you need to do a heck of a lot of legwork to get things to work - the difference is that (at least in this case) you cannot end up with unusable trash as the end result when you are just starting out.
Now, back to your question at hand.
Could you provide some screenshots for people to have a graphical look at what you are experiencing?
also a better descreiption of what you are attempting in more simple terms (I’m trying to get my running state to look injured for instance) may help everyone point you to different solutions.
As far as I know - additive animation basically takes the values of the bones in animation A and adds the values of animation B to it. This can obviously lead to issues with mesh deformation since the values may resolve as out of range for the mesh and you would really have no way of telling until you check the result.
Anyway, share some screenshots, I’m sure someone can land a hand or ideas at least.