I have a model which I rigged with the Mixamo addon (it's humanoid). Now I have to add a new bone (or something, probably it could be an object Empty) to make animation for ball (run with ball - new bone it was supposed to be for ball) and then a mesh will be added to the bone in Unity. I don't know how to do this. Once I added the bone to the armature and it worked with animation (but I think it wasn't control rigged bone) and in Unity animation doesn't work properly - this the bone animation.
So the problem was in unity,If you use humanoid rig it doesn't show extra bones in animators so in unity you should active this bones manual -> here is the answer https://forum.unity.com/threads/humanoid-rigs-and-extra-bones.360979/ If you have exportes file (fbx) with armature and baked animations in it In inspectore you have to go to animation tab -> go to MASK ( bottom in this window) then open transform tab and find bones wihich you want to be active in my case it was bone named *ball_control and then click apply _> in your export file it will create new animation xx_1 and this animation will show your extra bones.
Maybe someone use this