#he visibly took great pleasure in crushing Mario's spirit as much he did physically harming him

[pianokantzart]

Regarding your post on Bowser’s line, how would you want it to be addressed?

Either by Bowser targeting Luigi in order to follow through with his threat, or by Luigi being extra anxious about being used against his sibling. That line indicated that Bowser suspected from the beginning that Luigi, as Mario's brother, would be a point of emotional weakness. Now that he's witnessed the lengths they will go to protect each other, Bowser might be all the more inclined to make use of what he now knows for certain.