I kinda like Werner in the team just to keep the Madrid line from pushing too high. We are going into the match with an advantage. If Madrid don't score they are out and we have played really well defensively lately.
The best thing we can do is to cause gaps between their lines, Werner's pace keeps the cbs back with gives their midfield a dilemma. Push up and support the attackers press? If we can beat their first line and get the ball into pulisic/mounts feet they will repeatedly dribble pass Modric and Kroos as they did in the first leg. That's because the cbs left substantial space behind the midfield.
If the midfielders instead choose to sit deeper then Madrid's press will be ineffective as they'll be outnumbered. We will be able to keep the ball relatively comfortably- which is good for us.