I saw that this is added to Timeline in 2017.2 beta: Timeline: Added support for Avatar Masks on Animation Tracks. How do I access that feature? I do not see anything in Timeline itself, but I want to experiment with it to see if it will solve some issues in the game we are working on? Aside from that, I will add my voice as another vote for full additive blending in Animation tracks, not just override! Masking seems like a good first step for this, thus my investigation.