Contray to the other review here, I would argue (at least in four player) it is the worst treachery in the game. The potential to have it stay out for six+ turns, in a deck filled with horror, much of which is unavoidable, cannot be understated. Just one of these can easily cause 10+ horror across a team, and woe betide if you end up with two on the table at the same time. With two a guardian can go from full sanity to out of the game in a single mythos phase without even drawing from the bag. Brutal.