In my current D&D campaign, set in Critical Role’s Tal’Dorei setting, we have a player whose choices made me intervene and make his PC an NPC. Basically, he was playing a reskinned Raistlin Majere, but even more of a dick than the Raistlin in the novels. Things came to a head several sessions back, when, in a fit of rage at one of the other PCs, he murdered 19 townsfolk and fled the scene. So now we have a case of a PC that the player has NO INTEREST in redeeming, and, awesomely enough, supports the conversion of this character to an NPC.
This presented me a fantastic opportunity to make the rogue PC a castoff from the party AND have him come back to haunt them. His outrage and sense of mistreatment at their hands (his words) is what pushed him to committing mass murder, and he holds the party responsible for his actions. Not himself. So this is a character that has no interest in being good, no interest in being welcomed back, but, more importantly, no interest in going his separate ways. He wants revenge.
This led to a great session this past weekend, where the party has set out to their destination after having dodged the trap he set for them. Along the way, I felt inspired to really think about the character’s personality and motivations and how he would react to this, and his motivations of revenge and seeking power. Finding that the party dodged his trap, and that they were hot on his heels, he did what he has been prone to do: react and manipulate.
What was great fun was him not only scrying on the party, but then making his presence known to them, seeking to manipulate and undermine their group cohesion. This allowed me to really drive some great roleplay elements, and build on the tension leading up to the end of this quest, knowing that their former friend, and now nemesis, was hot on their heels, seeking revenge.