Is there a way to make toggling animation group mask smooth?

Hi all. I want to know if there is a way to make the toggling animation group mask smooth. for example, I’m playing idle animation, and when I enable the mask to exclude the spine (upper body), the upper body animations gradually lose effect and return to the rest pose and vice versa.

I think you will either have to use animation blending or weighting for that:

Masks are used to apply/exclude animations on targets, they are not related to how the animations are played.