I don't know. It feels like a big risk when we don't even know what the reward is going to be.
Do you think— whatever Boothill's monster is, do you think he and his partner were both affected? Or did it just pick one or the other because their link wasn't confirmed?
I don't know... If his partner was affected, surely they would be one of the other people who were active that night... either Aventurine, or the person who killed Death.
And if they weren't... maybe it's as you say. A coin flip, once the monster is summoned.