I think there is some bug with the facesitting stance, I was trying to get the enemy doing it and when it happens the enemy go facesitting stance while I don't get forced into it. The commands then become weird, since I can stand up or roll while the enemy is still in facesitting.
Also, can I ask the conditions of getting facesitted, if any?
Seems like it gunks up when you trip at the same time. The whole force-stance switching and enemy tripping routine needs some love so that it'll be bug-free; right now it's a little hacky, so it's no surprise there's a few kinks in it.
Enemies will sit on your face currently if they're not a centaur (of either type), you're Supine, and they're not already erect.
