I'm pretty sure he meant Ridden; you know, humans playing host to spirits in Werewolf? Interestingly, sin-eaters look suspiciously like Ridden to werewolf senses, which can sometimes put them at odds with one another.
Forgotten threshold, most likely. I've got one Forgotten who died when a chunk of falling satellite lodged itself in his brain. As for the most senseless death ever... Hmm, I'm not sure. Maybe a string of unfortunate events, one right after the next, until one finally killed him?
Could be. Might be a Reaper, too, planning to hunt down those he believes are behind his series of unfortunate events.