Have you insights about what is important to the target? Like, really really important?
Take that away. Target his career. Or his social life. Or his looks. Everything he draws joy and peace from.
What @A_Pariah said. Also maybe try to turn the tables and get something bad on him. If people wanna play dirty, you should take them to school. Many ways a woman can do this.
Glasya-Labolas can give him a brutal death if you want him to suffer but you also have to specifically tell Labolas to only kill that one person-he’s known for being very very messy and very very much the author of manslaughter and bloodshed