This foe has placed their soul into a magical item, protecting them from Death. The only way to kill them completely is to break the item and destroy the soul within. When you destroy the soul container to try to kill the soul inside this foe is killed outright but you are caught in the vengeful backlash of Death itself, roll+CON. On a 10+ you take -1 forward to Last Breath. On a 7-9 you take -1 ongoing to Last Breath until you can break this curse. On a 6- you roll Last Breath immediately.
Horcux, anyone? I really wanted to write a move that involved Last Breath, but it needed to be something the players were aware of before they triggered the move. Having a player automatically roll Last Breath is the hardest of hard moves, so I wanted the player to know what they were getting into before trying to trigger the move. The potential result also needed to be worth the risk.
To address the first point, I wanted to write the trigger such that the move couldn’t be triggered by accident. If you find the crystal ball that holds the soul and you don’t know the soul is inside, it wouldn’t be fair to suddenly have the player roll this move simply because they dropped the ball into the trash and it shattered. Adding “to try to kill the soul inside” made it more explicit.
For the second point I think I’ve made the reward pretty good here: you win. The key thing will be making sure that the Soulbox is actually a viable option when fighting this enemy. No point in going on wild Harry Potter chase for a tiara or locket if you can just hit the guy in the face with a hammer and call it a day.
I’m not entirely sure about the difference between the 7-9 and 6- results. I like rolling Last Breath immediately but I’m not sure about -1 ongoing. -1 ongoing seems almost harsher, depending on how many times you end up rolling Last Breath.