A free mod for Witcher 3, by Maciej Polanski.
This mod is a simple one, but very useful for those who want to have a better and faster reaction time. The idea is simple: press the right mouse button and you'll be able to block and dodge in the same way as if you were using the arrow keys. This allows you to get more precise with your movements, and the reaction time is reduced.
It also works for enemies: if you're trying to attack and you're standing still, you can use this to your advantage. It's very easy to use, so it's a good idea to try it out.