Hello!
Our animator used inner spine mask for new spine-character (v.3.6.x), but in Unity (2017.3.1p1) it produced very low performance.
On my PC I had 180-200ms CPU time!!! :o 5 FPS only from one spine-character.
I did profiling and found so slow function - SkeletonClipping.ClipTriangles.
So... What we need to fix that problem?