Thar be spoilers down below, ahoy.
Cruel mercy, I feel, is more fitting for revenge. Death is quick and although it punishes the person that's done you wrong,
I feel like sometimes, it's not enough of a payment.
For example, the Overseer.... branding him as a Heretic effectively makes him a pariah and a social outcast, forced to live in
the sewers and rejected by ALL, stripped of everything that he had gotten through his machinations. He is forced to spend
whatever time he has left dwelling on everything that's lead up to that point, with nothing but despair to keep him company, wondering
when he will succumb to the plague.
MUCH more effective.