A free mod for Witcher 3, by va.
A mod from the cdproject forums allows you to increase the speed of animations for Combat Skills.
A couple of skills from the combat skill tree can be modified in this way. The maximum speed of animations increases by 10% per level, up to a maximum of 50%.
And that's all, you don't need any other files for it.
It's very simple, the proper way to increase animation speeds is to edit Behavior variables, but I didn't have any luck there, so this is a workaround until there's a way to edit behavior files.
